THE CHILEAN TSUNAMI OF MAY 24,1960 ‐ 【津波ディジタルライブラリィ】

Preface

In the early morning of May 24, 1960 (J.S.T.), all coasts of Japan were attacked by a tsunami which was originated in Chile on the preceding day. The tsunami reached a height several meters above M.S.L. on the Pacific coast of Hokkaido and the N. E. Honshu, resulting serious damage to houses and properties. The tsunami was felt even on the coast of the Japan Sea.
Although we have felt several times the tsunamis which were originated in the Chilean water in these hundred years, damage caused by these distant tsunamis was not so remarkable as the recent one since the wave heights used to be less than two meters.
The protective measures against tsunami have developed quickly since the 1933 tsunami, but they aimed mainly at near tsunamis which occur in the neighboring seas of this country, and the study of distant tsunamis has been neglected. The present Chilean tsunami differs much from the near tsunami in that it was felt on all coast of Japan and that it had a long period of over one hour, showing very different coastal effects, and resulting unexpected damage at places which had been safe for near tsunamis.
The tsunami was not only a very rare one but also gave a good chance to know the effect of various protective structures against different tsunamis.
Soon after the occurrence of the tsunami damage, a field investigation committee was organized, with the cooperation of the members of the Japanese Organization for Tsunami Investigations (JOTI) and geophisicists of the universities in all districts of Japan. The number of investigators amounted to one hundred. Before going out for the investigation,
a discussion was made by main investigators about the method and items of survey to make the results of investigations uniform.
A provisional report of the investigation has been published by mimeographic print and distributed among Japanese researchers to serve for their research works. This monograph is the revised edition of the provisional one, with additional photographs and original research papers. The rusume of the field investigation report, names of localities, and explanations of photographs have been translated into English, except for field notes, for the use of foreign researchers.
Expenses of field investigations and the publications have been defrayed partly by the Ministry of Education and partly by the Japanese Organization for Tsunami Investigations, to the officials of which our tanks are due. Records of tidegauges have been put to our disposal by the courtesy of the Japan Meteorological Agency, the Japan Geographical Survey, the Hydrographic Office, the municipal offices of different prefectures and the regional offices of Public Work Construction Office. During the course of investigation, we could freely avail the cooperation of officials in town and village offices in gathering informations and other materials. On behalf of the Investigation Committee, I should like to express my hearty appreciation to the cooperation of these gentlemen. My thanks are also extended to Mr. Tokutaro Hatori for his effort in compilation of the materials, without which this monograph could not be published.
August, 1961.
Ryutaro Takahasi
Chairman of the Committee for the Field Investigation of the Chilean Tsunami of 1960.

The Committee for the Field Investigation of the Chilean Tsunami of　1960 チリ津波合同調査班調査者氏名

北海道大学
福富孝治鈴木建夫清野政明村瀬勉藤木忠美須川明柏村正和
八鍬功高橋将大谷清隆中村勉
東北大学
加藤愛雄高木章雄伊藤三吉中村公平江村欣也西城忠泰近藤実
(気仙沼水産高校)
鈴木次郎石田治子加藤盤男阿部正宏島田豊郎阿部宏植田良夫
鈴木光郎青木謙一郎福井英夫渡辺良雄長谷川典夫藤原健蔵岩井淳一
高柳洋一中川久夫佐藤値小貫義雄柴田豊吉三位秀夫田村美乃
北村信小高民夫片岡純森啓菅原捷
東京大学地震研究所
高橋龍太郎河角広佐藤泰夫表俊一郎小牧昭三桃井高夫黒木義弘
笠原慶一茅野一郎平能金太郎平沢朋郎相田勇影山正樹羽鳥徳太郎
(東京大学理学部) (東京大学理学部) (東京大学工学部)
高隆二山口林造岡田惇
(東京大学工学部)
東京大学理学部
高野健三佐藤良輔栗本広高野敬寺本俊彦永田豊須藤英雄
竹田厚
東京大学工学部
堀川清司鮮干撤
東京水産大学
三好寿山口和貞
東京学芸大学
冨永　政英
名古屋大学
飯田汲事島津康男青木治三熊沢峰夫太田裕成瀬聖慈
京都大学理学部
速水頬一郎国司秀明福尾義昭
京都大学防災研究所
椹木享樋口明生吉田幸三柿沼忠男谷泰雄久下元一
九州大学
下鶴大輔後藤賢一種子田定勝
気象庁
宮崎正衛宇野木早苗土屋瑞樹
海上保安庁水路部
川村文三郎茂木昭夫新田清高田四郎土屋孝佐藤照雄永野真男
日本建築学会
代表者武藤清 (順不同)

1. Photographs

写真 Fig.1. Kiritappu,Hokkaido: Kiritappu is a Iand-tied island. There,the forerunners of the destructive waves had been found out by inhabitants. They climbed the neigh. bouring hill and Iooked down

写真 Fig.2. Kiritappu,Hokkaido: View from the opposite side to that of Fig.1. The town was completely destroyed. The sand bar forming a Iand-tied island was cut by the torrent and the town was left i

写真 Fig. 3. Kiritappu, Hokkaido: The panorama photograph of the new strait taken from the isolated town, after the sufficient time passed by from the attack of Tsunami. The sea between the two broken line

写真 Fig. 4. At Shoya, Hokkaido, they had been digging an empty dike to enlarge the harbour. The Tsunami destroyed the barrier standing between the harbour and the empty dike. Nearly twenty fishing boats a

写真 Fig. 5. View after the recession of the same wave as that shown in Fig. 4, at Shoya, Hokkaido. (Courtesy of Mr. Chutaro Ikeno, Shoya.).

写真 Fig. 6. Kelps left by the recession of the wave at Muroran, Hokkaido. (Courtesy of the Institute of Algologi- cal Research of Hokkaido University.)

写真 Fig.7. Inside part of the wharf bored by the torrent receding seawards at Urakawa, Hokkaido. (Courtesy of Urakawa Harbor Construction Office.)

写真 Fig.8. Torrent receding seawards at Hakodate, Hokkaido. The horizontal line shown by the arrow is the highest water mark.(Courtesy of Hokkaido Times.)

写真 Fig. 9. Tsunami running into the Same Harbour, Hachinohe,Aomori Pref.

写真 Fig.10. Fishing boats thrown up on the shoal off Hachinohe, Aomori Pref. (Courtesy of The 2nd Air Wing, Hachinohe.)

写真 Fig.11. Tsunami running upstream at the mouth of Niita River, Hachinohe, Aomori Pref. at 9 h 30 m, May 24. (Courtesy of Mr. Fusao Tabata.)

写真 Fig.12. Neighborhood of the fish market at Noda, Iwate Pref. (Courtesy of the Village House of Noda)

写真 Fig.13. Neighborhood of the mouth of Kuji River, Minato, Iwate Pref. Sea wall seriously damaged. (Courtesy of Iwate Nippo.)

写真 Fig.14. Miserable plight of Takahama, Miyako, Iwate Pref. (Courtesyof Iwate Nippo.)

写真 Fig. 15. Trace of the Tsunami marked on the white wall of a house at Akamae, Miyako, Iwate Pref. (Photo taken by M. Tsu- chiya.)

写真 Fig. 16. House destroyed by a boat running up on the shore at Ori- gasa on the Bay of Yamada, Iwate Pref. (Courtesy of Iwate Nippo.)

写真 Fig.17. Sea breaker broken down at the northern Coast of Funakoshi, Iwate Pref.(Photo taken by K. Horikawa.)

写真 Fig.18. Road broken down at Negishi on the Bay of Otsuchi, Iwate Pref. (Courtesy of the Municipal House of Kamaishi.)

写真 Fig.19. Neighborhood of the Kamaishi Custom House at 5 h 00 m, May 24.(Courtesy of the Municipal House of Kamaishi.)

写真 Fig.20. Reflux in the neighborhood of the Kamaishi Custom House. (Courtesy of the Municipal House ofKamaishi.)

写真 Fig. 21. House crushed down by a fishing boat at Ofunato, Iwate Pref. (Courtesy of Asahi Shimbun.),

写真 Fig. 22. Wretched sight of Ofunato, Iwate Pref. (Courtesy of Asahi Shimbun.)

写真 Fig. 23. Trace of the Tsunami at Ofunato, Iwate Pref. (Photo taken by Y. Sato.)

写真 Fig. 24. Railway washed away from the bal-last which was constructed under the truck in profile at Otomo on the Bay of Hirota, Iwate Pref. (Photo taken by I. Kayano.)

写真 Fig. 25. Railway washed away by the Tsunami and fishing boats left on it at Kesennuma, Miyagi Pref. (Courtesy of Yomiuri Shimbun.)

写真 Fig. 26. First wave of the Tsunami ascending Kize River, Kesennuma, Miyagi Pref. (Courtesy of a citizen of Kesnnuma.)

写真 Fig. 27. A huge number of driftwoods and damaged houses at Shizukawa, Miyagi Pref. (Courtesy of Yomiuri Shimbun.)

写真 Fig. 28. House turned upside down by the Tsunami at Shizukawa, Miyagi Pref. (Courtesy of Asahi Shimbun.)

写真 Fig. 29. Flooding by the fourth wave of the Tsunami at Onagawa Railway Station, Miyagi Pref. at 4h 45 m, May 24. (Photo taken by M. Kondo.)

写真 Fig. 30. Ships pushed against the bridge girder at Ishinomaki,Miyagi Pref. (Courtesy of Asahi Shimbun.)

写真 Fig. 31. Sightseeing boats left on a street by the Tsunami at Shiogama, Miyagi Pref. (Courtesy of Yomiuri Shimbun.)

写真 Fig 32. Abnormally low water caused by the Tsunami at Nakaminato, Ibaraki Pref. at 5 h 41 m, May 24. (Courtesy of Nakaminato Koji Jimusho, Ibaraki Pref)

写真 Fig. 33. Surging Tsunami at Nakaminato, Ibaraki Pref. at 6 h 15 m, May 24. (Courtesy of Nakaminato Koji Jimusho, Ibaraki Pref)

写真 Fig. 34. Tsunami surging into the Onahama Harbour, Fukushima Pref. at 5 h 00 m. (Courtesy of Mr. M. Onoda.)

写真 Fig. 35. Tetra-pods of 4 tons washed away by the Tsunami at Iioka, Chiba Pref. (Courtesy of Choshi Doboku Shutchyojo.)

写真 Fig. 36. Driftage left on the beach by the Tsunami at Sakata, Chiba Prei. (Photo taken by R. Yamaguchi)

写真 Fig. 37. Well arranged rafts cultivating the pearl oysters in the Bay of Matoya, Matoya, Mie Pref. before the attack of Tsunami. (Courtesy of Mr. T. Sato)

写真 Fig. 38. Rafts scattered by the Tsunami in the Bay of Matoya, Matoya, Mie Pref. The ships are feeling for the pearl oysters missed at the sea bottom. (Courtesy of Mr. T. Sato)

写真 Fig. 39. Utter confusion of the Shimizu Harbour, Shimizu, Shizuoka Pref. caused by stray timbers. (Courtesy of Yomiuri Shimbun.)

写真 Fig. 40. Entrance of the Harbour of Owase, Mie Pref. at 5 h, May 24. (Courtesy of Owase Doboku Jimusho)

写真 Fig. 41. Highest water time at Owase, Mie Pref. The Tsunami is sweeping into the city with stray timbers and cans. (Courtesy of Owase Doboku Jimusho.)

写真 Fig. 42. Bank broken by the Tsunami at Nansei, Mie Pref. (Photo taken by H. Aoki.)

写真 Fig. 43. Wharf destroyed and washed away at Tanabe, Wakayama Pref. (Courtesy of the Municipal House of Tanabe.)

写真 Fig. 44. Rafts cultivating the pearl oysters, piled by the Tsunami in the Bay of Tamaura, Wakayama Pref. (Courtesy of Uragami Gyogyo Kumiai.)

写真 Fig. 45. Damage of the railway caused by stray timbers at Susaki, Kochi Pref. (Courtesy of the Municipal House of Susaki.)

写真 Fig. 46. Ship cast up on the dry land by the Tsunami at Susaki, Kochi Pref. (Courtesy of the Municipal House of Susaki.)

写真 Fig. 47. Man showing the highest water mark on the wall of a primary school by his left hand, at Haji, Okinawa. (Photo taken by S. Taneda).

写真 Fig. 48. Bridge broken by the Tsunami at Haji, Okinawa. (Photo taken by S.Taneda.)

2. Papers

A Summary Report on the Chilean Tsunami of May 1960

1. A historical sketch of the Chilean earth-quakes

In the early morning of May 24, 1960, an enormous tsunami, originated in the sea off the coast of Chile, and was propagated across the Pacific Ocean, attacked the Japanese Pacific coast. As the result of it, cities, towns and villages on the Pacific coast of Japan, especially those in Hokkaido and the Sanriku district suffered severe damage.
Although the present Chilean earthquake was of an exceedingly large magnitude, M being estimated 8(1/2), it was not, of course, felt by the human senses in Japan. The attack of the present tsunami was therefore a great surprise for the coastal inhabitants, because tsunamis are usually preceded by an earthquake with slow but long-lasting vibrations.
We will enumerate in the following some historical tsunamis which originated in the sea of Chile, and will list those which gave some effects on the Japanese coast, as described in different ancient documents of Japan.
According to K. Horikawa3.24) 27 tsunami earthquakes have occurred in the sea near Chile during the years 1500-1960 as listed in Table 1, A.
The 1837 tsunami has been added from other source. Beside these tsunamis many distant tsunamis, especially those originated in Japan, have been felt in Chile, but only recent ones were listed in B above.
Among the tsunamis caused by these earthquakes listed in Table 1, A following tsunamis were felt in Japan with the effects as remarked.
Those tsunamis of 1837, 1868, 1877 and 1960 caused respectively remarkable damage in Hawaii, too.

写真 * The Earthquake Research Institute. University of Tokyo.

2. The earthquakes

An earthquake of magnitude 7(1/4)-7(1/2) (Berk) took place near Lebu, central Chile, at 1002 on May 21, 1960 (U.T.). The earthquake caused casualties and damage to buildings and other stru ctures at Concepcion and surrounding. A weak tsunami was also caused and has been recorded at Talcahuano. This earthquake may be regarded as a foreshock to the main one on May 22. On May 22, there occurred three moderate earthquakes, each of magnitude 7-7(3/4), to the south of the earthquake of the preceding day. The times of occurrence were 1032, 1910 and 1911. The main shock, which shaked the whole globe, occurred 30 sec. after the last shock, that is, at 19h llm 20s. The epicenter of this main shock, as estimated provisionally by US Coast and Geodetic Survey4), are at 38^oS, 73(1/2) W. The magnitude was first reported 8(3/4) and later revised 8(1/2) (Berk).
All of these earthquakes have been observed in Japan, too, at Mt. Tsukuba and Matsushiro Observatories. The position of the epicentre of the main shock seems to be less accurate, because the initial part of the main shock has been masked by the tail of the preceding shock. The aftershock area has been found to extend as far as 50ーS. According to the field investigation of the writers, the macroseismic area of the main shock extends from the Province of Caution down to the Province of Chiloe, an area extending to 200 km x 500 km.
The land near Lebu has risen by about 1 m and the lands arround Valdivia and Ancud in Chiloe Island have subsided by 1.6 m and about 1 m. respectively. It is reported that a land upheaval was observed to the south of Chiloe Island. These land deformations must be a part of the dislocation which took place in the sea. Just as in Japan, shallow earthquakes in Chile occur mainly on the coast or in the Continental shelf just outside of the land. Earthquake focii deepen towards east. It is very natural therefore to assume that a sea bottom dislocation took place on the continental shelf, probably between Con- cepcion (37^oS) and Castro (43^oS). Readers refer to Fig. 1.

表 Table 1. Earthquakes that caused tsunami on the coast of Chile during 1500〜1960.

地図 Fig. 1.

3. Propagation of the tsunami caused by the earthquake

In Fig. 2 are shown the distribution of initial motions of tsunami (・... Upwave ; o. . . . Down wave) and the arrival time (GMT) of the wave front. The initial motion began with an up- wave at almost all stations, excepting several ones in Alaska, Aleutian Is- lands and Hokkaido. At these stations initial motions seem to have been down-waves but are not very distinct owing to the superposition of bay seiches.
From the distribution of the initial motion, the sense of the sea bottom dislocation may be concluded: the sea bottom upheaved on the northern, southern and western parts of the dislocated area, while the bottom sank at the eastern and central parts of the same area.
The arrival time was taken from many sources; the Preliminary Report, U.S. Coast and Geodetic Survey, the Provisional Report of the Japanese Investigation Committee(l)), and other informations which were kindly given, by authorities in different countries, to Japanese Organization for Tsunami Investigations.
The tsunami waves, as seen from the arrival time, seem to have been propagated through Pacific Ocean by three paths: northern Pacific; southern Pacific via Christmas Is. ; Johnston Is. ; Wake Is. ; and southern Pacific via Samoa Is. and Canton Is. It is interesting to see that for Tasmania, Sydney and Brisbane, the tsunami waves are propagated via the antarctic sea south of New Zealand.
The arrival times, as shown in Fig. 2, are almost the same as predicted by refraction diagram drawn by Dr. T. Hirono26). In Fig. 3, we have shown the inundation heights and arrival time of the wave front on the Pacific coast of Japan. The tsunami was felt most early at Miyagi-Enoshima (1718 GMT), and then at Kushiro, Hokkaido and Hachijo Island.
The tsunami waves seem to have attacked the N. E. Honshu from a direction almost normal to the general trend of the coast, the arrival time being nearly the same at each stations in this region. A similar feature of the wave front arrival can be seen on the roast from Kisyu to Kyushu in S. W. Hon- shu. The arrival times at this coast are 1 hour behind those on N. E. coast.
Seen from the arrival time, the tsunarni front seems to have suffered a little delayin passing through the sea bottom ridge which extends from Izu peninsula down to Marianas Islands. A similar delay in the arrival time of tsunami front can be noticed at Ryukyu Island chain.
The inundation heights, given also in Fig. 3, are of the order of 2 m along the N. E. coast, although in some places it was as high as 3.2〜3.8 m. In contrast with this, the in- undation heights on the S. W. coast are of the order of 1.3 m. everywhere. The differ- ence may be attributed to the effect of the Izu-Marianas ridge which the tsunami waves had to cross to reach the S. W. Japan.
The refraction diagram drawn by Dr. T. Hirono shows the convergence of tsunami energy at Japanese Coast. A rough estima- tion shows that the energy density along the N. E. Coast of Japan is approximately one third of that at the Chilean coast. This means that the ratio of wave heights to be ten. According to withnesses, the inunda- tion height at Isla Macha, Chile, is said to have been over 20 m., and that at Mehuin 15 m. Then it is not unreasonable that we had the inundation height of 2.0 m on the N. E. coast of Japan.
In Table 2, are listed the maximum amplitude and the corresponding period of the Chilean tsunami as read off the tide-records, some of which have been collected by U.S.C.G.S.4) and some have been kindly put to our disposal by the courtesy of the authorities concerned.
The inundation height along the coast of Chile that was measured by K. Horikawa and ourselves is listed in Table 3.
Table 4 is the list of inundation heightof tsunami above MSL, the average period, the arrival times of the wave front and the arrival time of highest wave, at principal tide-stations on the Pacific coast of Japan.

地図 Fig. 2.

地図 Fig. 3. May 22, 1960 CHILE TSUNAMI Inundotion Height (m) Arrival time of the initial rise or fall. (GMT)

表 Table 2.

表 Table 3.

表 Table 4.

4. The waee-form of the recent Chilean tsunami

It has been noticed since the Sanriku tsunami of 1933, or the Kamchatka tsunami of 1952, that the records of tsunami obtained at distant stations situated on the circum- ference of the Pacific ocean have generally spindleshaped envelopes, while at near stations or at oceanic island stations, the envelopes are triangular. This fact has been explained by the present writers as follows: There are two kinds of waves that consist a record of tsunami. One is the wave train which is propagated directly from origin to the station. This wave train has a triangular envelope. Another is the wave train which reaches the: station after reflecting at the coast. The number of reflection may be any. The waves change themselves into dispersive epiconti- nental waves as the number of reflection increases, and are propagated along the coast. This wave train has a spindle-shaped en- velope. The time which is needed for the wave train to build up to the maximum amplitude seems to depend linearly on the travel time of the wave front to the station. For instance, in the Kamchatka tsunami, the build up time B is connected with the travel time t by the relation (B=3.1+0.2 t. At some places both kinds of wave train are mixed up
In the case of the recent Chilean tsunami, the shape of the envelope of the wave train was triangular everywhere. This seems to mean that a most part of the energy of the tsunami was emitted normally outward from the coast and a very small portion of the wave energy was emitted along the coast. According to the results of model experi- ments, tsunami energy is emitted more into the direction of the shorter diameter of the elliptic origin than in the direction of the longer diameter. Considering that the origin area of the Chilean tsunami is elongated along the coast of Chile, the above explanation seems to be consistent. Surprisingly quick decrease of the inundation height on the Chilean coast with the distance from the origin area may favor this explanation, too.
The identification of waves on the records obtained at adjacent stations seems to be possible up to the fourth wave if we smooth very short waves in the records. The second trough was very low everywhere in Japan. The most tide-gauges in N. E. Honshu failed to record this trough but the sea was estima- ted to have ebbed by 2〜3 m. Seeing this abnormal ebb, inhabitants on the coast could think of the tsunami and evacuated before a tsunami warning was issued by officials. Such an abnormally large ebb as this is a rare phenomenon which was not noticed even in the case of the great Sanriku tsunami of 1933, and is worthy of special mention.
As to the period of the tsunami waves, we can notice the general predominance of the periods 60〜80 min. At several stations in Central and South America and Hokkaido, Japan, however, a very long period of 3 hours has been observed. On the contrary, on all the oceanic islands in the Central Pacific ocean, tsunami records are superposed by short-period disturbances [of about 10 min., which are probably the island seiches or the seiche of the lagoon inside the reef.

5. The spectra of the Chilean tsunami at different stations along the Japanese Coast

A spectral analysis was made about the tsunami records obtained at 17 stations, well distributed from Hokkaido to Kyushu. The tide-gauges at these stations are mostly of the same type. In Fig. 4, are shown the spectra of these records.
As can be seen in the Figure, all spectra are composed of several peaks and a continuous back-ground. Some of the peaks are common to most of the stations suggesting that they are characteristic of the tsunami. The continuous back-ground increases in intensity, proportionally to the period up to a certain limiting period, and then it rapidly fades out. This implies that there is an upper limit in the period of the tsunami spectrum, and the energy of the back-ground is uni- formly distributed to every period below this limit. This upper limit period coincides practically with the effective period Te of the tsunami.
The shaded column in Fig. 4 shows the period of seiches at that station.
It is remarkable that the features of tsunami spectra for N. E. Japan are different from those for S. W. Japan. In the former region, spectra have the common and highest peak at 80 min. and a second peak at 40 min., whereas in the latter region, spectra show the highest common peak at 40 min. The peak at 80 min. is very weak in this region. This difference of the spectral feature for the two region might be attributed to the reflection of the tsunami at the Izu-Marianas ridge which separates the two region. As can be proved mathematically, the long period components of the wave spectrum must be reflected more than the short period compo- nents when the tsunami wave pass through the ridge.
According to Dr. K. Kajiura23), the reflec- tion of tsunami wave at a ridge is most effective when the breadth of the ridge is 1/10〜1/5 of the wave length. In this case, since the period is 80 min. and the depth 4,500 m, the wave length becomes 1,000 km, while the breadth of Izu-Marianas ridge is about 100〜150 km. So the reflection must have been very effective for the 80 min. component of tsunami wave. This explanation is very consistent with the difference in wave heights of tsunami in the two regions.
An alternative explanation for the rather low inundation height between Izu and Kii peninsulas in the Central Honshu is the oblique incidence of the tsunami waves for this part. In this case, only a fraction of the wave energy reaches the coast as the geometry simply proves it.

地図 Fig. 4. Spectra of the Chilean tsunami of May 24, 1960

6. Topographic effects

The present tsunami is the only distant tsunami that was observed with pretty large amplitude on Japanese coast. Many charac- teristic features have been observed which are entirely different from those of near tsunami.
In the case of the recent Chilean tsunami, the entire coasts of Japan, not only the Pacific coast, but also the Japan Sea Coast, felt the tsunami; whereas in the case of a near tsunami, it is felt only at a limited part of the coasts. The Sanriku tsunami, which occurs in the N. E. Pacific of Japan, usually does not affect the S. W. Coast, and vice versa.
Since a near tsunami includes short period waves of comparatively large amplitudes, topographic effects becomne remarkable. Among these topographic effects, squeezing of wave energy in triangular bays, and the decay of wave energy in shallow and long bays were recognized so evidently that we erroneously thought these phenomena uni- versal to all tsunamis. In the recent Chilean tsunami, which had very long periods of 80〜40 min., and no remarkable short period waves, the squeezing effect was not remark- able in triangular bays which have generally short proper periods. The inundation heights were almost the same everywhere in the bay. The squeezing effect worked, however, to some extent in some large bays which have long proper period over 40 min. The bays of Hirota, Ofunato, Onagawa and Shizu- kawa are such ones. In these bays the in- undation at the head of the bay was twice as high as at the month. The current due to the tsunami had a velocity a little larger than the ordinary tidal current.
The Chilean tsunami reached a considerable height of more than 5 m above M. S. L. at several places between Hachinohe and
Taneichi in the N. E. Japan. The coast is quite straight in this part, so we cannot attribute the cause of this inundation height to the squeezing of wave energy. The only possible cause is the concentration of wave energy to this part of the Pacific coast. The refraction diagram prepared by Dr. Hirono clearly shows the energy concentration to this place. A rough estimation showed for this place an energy density some 1/4 at the Chilean coast. This means a wave height half as high as at the Chilean coast.
In such a large bay as Tokyo or Ise, at which the period of seiches is more than 60 min. and the month is pretty narrow, the tsunami reached higher places at the month of the bay than at the head.
In the S.W. Japan, inundation heights were generally low compared with those in N. E. Japan, as was mentioned above. They were of the order of 3.5 m for bays with proper periods of 30 min. or more, but were of the order of 1.5 m for bays with shorter periods. For straight coasts they were 1〜1.5 m as mentioned above.
In the tsunami record obtained at capes such as Mera, Omaezaki, Kushimoto or Tosashimizu, short-period oscillation with period 20〜30 min. is remarkable. The amplitude of these oscillations are large compared with the wave amplitude in the neighbourhood. At Naze, S. W. Island, tsunami attained at the maximum height of 4.5 m, a remarkable value considering that the inundation heights at other islands are much lower than this value.
The Chilean tsunami has shown, in this way, many characteristic features about the coastal effect which had not been experienced by near tsunamis.

7. Damage

The present Chilean tsunami made tremendous harms to Chilean coast, Hawaiian coast and Japanese coast. In the following, we will describe briefly the damage Japanese coasts sustained.
Since we have experienced very few distant tsunamis in the past, and since they seldom did harm to human lives and properties, all protective measures in Japan have been made against near tsunamis. For the present Chilean tsunami of different characters, pro- tective structures had been insufficient at such places where only slight damage had hitherto been caused by ordinary near tsunamis.

表 Loss of lives caused by the tsunami was as follows:

表 The dath tolls caused by recent tsunamis in Japan will be listed in the following for a reference.

表 The main damage to houses and other properties are listed as follows

8. Epilogue

Among the recent tsunamis that took place in the circum-Pacific zone, following ones gave some effect to remote coasts distant more than 1,000 km from the origin: the Aleutian tsunami of April, 1946; the Kam- chatka tsunami of Nov., 1952; the Aleutian tsunami of Mar., 1957; and the recent Chilean tsunami of May, 1960.
Among these distant tsunamis the 1952 and 1960 tsunamis caused damage at Japanese coast. The 1952 tsunami showed an amplitude of several tens of centimeter at all Japanese tide-stations. Some damage wascaused in Hakkaido and Sanriku district by this tsunami.
In Hawaii, damage was caused by the tsunamis of 1946, 1952, 1957 and 1960 cited above. The wave height as large as 13 m was observed at Haena, Kauai Island, in the case of 1946 tsunami.
Beside these tsunamis, the Peruvian tsunami of Nov. 20, 1960 has also been felt in some tide-stations in Japan. Distant tsunami is never a rare phenomenon. The writers wish to bring to light the further characteris- tics of the distant tsunamis as well as those of near tsunamis, in order to contribute to the improvement of counter measure against these disasterous phenomena.

References

1) Field Investigation Committee for the Chilean Tsunami. Provisional Report on the Chilean tsunami of May 24, 1960. July, 1960. (In Japanese)
2) Architectural Institute of Japan: Supplementary Reports to (1). (In Japanese)
3) HORIKAWA K.: The outline of the investigations of the Chilean tsunami in Chile and other countries. (In Japanese) Kaigan (The Sea Coast) No. 28.
4) SYMONS, J. M., B. D. ZETLER: The Tsunami of May 22, 1960 as Recorded at Tide Stations. Preliminary Report, U.S. Dept. of Commerce, Coast and Geodetic Survey.
5) TAKAHASI R.: Report on the Chilean Tsunami of 1960. Proceedings of the Second World Conference on Earthquake Engineering. Vol.1., Japan 1960.
6) IWASAKI T., K. HORIKAWA: Tsunami Caused by Chile Earthquake in May, 1960 and Outline of Disasters in Northeastern Coasts of Japan. Coastal Engineering in Japan, Vol. 3, Dec. 1960.
7) HORIKAWA K.: Some Additional Remarks on the Chilean Earthquake Tsunami, Coastal Engineering in Japan. Vol. 3. Dec. 1960.
8) The Hilo Tribune-Herald: The Big Wave, May 23, 1960.
9) SASAKI S: On the Chilean tsunami (In Japanese) Proceeding of the 7th Symposium on Coastal Engineering, 1960.
10) IWASAKI T., and K. HORIKAWA: Outline Of the damage in the Sanriku district caused by the Chilean tsunami (In Japanese) Journ. Japan Soc. Civil Engineers 45 (1960).
11) HORIKAWA K: Report on damage caused by the Chilean tsunami. (In Japanese) Proceeding. 4th Symposium on Earthquake Engineering. 1960.
12) Architectural Institute of Japan: Special Volume for the Chilean tsunami, Journ. Archit. Inst. Japan. 75 (1960).
13) Tohoku Kaihatsu Kenkyukai (Research Comm. f. Development of N. E. Japan): Special Vol. for the Chilean tsunami, Tohoku Kaihatsu (Developing N. E. Japan) 10 (1960) No. 5.
14) MIYOSHI H: Capes and Tsunami (In Japanese) Shizen (Nature) 16 (1961).
15) NAKAHARA H: The Chilean tsunami as I saw it (In Japanese) Kisho (Weather) No. 42. (1960).
16) FUKUOKA M., M. HOSOI, H. YOSHIKAWA, T. KINOSHITA, N. SUTO and T. BABA: Report of the investigation on the Chilean tsunami. (In Japanese) Technical data for Public Works 2 (1960).
17) WATANABE H.: On the propagation and convergence of the Chilean tsunami of 1960. (In Japanese) Umi to Sora (The sea and Sky) 37 (1961).
18) Sendai Meteorological Observatory: Report on the field investigation for the Chilean tsunami of 1960. (In Japanese). 1960.
19) Hachinohe Harbor Construction Office, Ministry of Transportation: Collection of data concerning the Chilean tsunami at Hachinohe Harbor and vicinity. (In Japanese).
20) WIDEN S.O.: Tsunami of May 22, 1960 West Coast of Canada, Canadian Hydrographic Service.
21) WATANABE T., J. KARZULOVIC KOBOT, Los Movimientos Sismicos del Mes de Mayo de 1960 en Chile. Univ. d. Chile Publication No. 14, Ano 1960.
22) DOBROVOLNY E., R. LEMKE, W. BOWES, H. THOMAS, y N. BRAVO: Relacion entre la Geologia y el Dano broducido por el Terremoto del 22de Mayo de 1960, En Puerto Montt, Chile. Instituto de Investigaciones Geologicas. (Informe Preliminary).
23) KAJIURA K.: Paper to be read at the HIG Tsunami Hydrodynamics Meeting, Hawaii, 1961.
24) HORIKAWA K: The Chilean Earthquake and Tsunami (In Japanese) Proc. Symposium for Prevention of Disasters 1960.
25) EATON J. P., D. H. RICHTER and W. U. AULT: The Tsunami of May 23, 1960, on the Island of Hawaii. Bull. Seismological Society America, Vol. 51, No. 2. 1961.
26) The Japan Meteorological Agency, Tokyo: The Report on the Tsunami of the Chilean Earthquake, 1960. (In Japanese) Technical report of the Japan Meteorological Agency, No. 8, 1961.
27) JAMES N. JORDAN: Some Aspects of the Chilean Earthquake of 1960. Geotimes Vol. 5, No. 5, 1961.
28) IWASAKI T., A. MIURA and S. TERADA: On the Effect of the Breakwater in Case of Tsunami, Part 1 (The Model Experiment of Tsunami in Kesennuma Bay). Technology Reports. TOHOKU Univ. Vol. 25, No. 2, 1961.

Seismological Data of Chilean Earthquakes in 1960

abstract

1960年5月21日よりチリ地域において地震活動が活発になり,なかでも5月22日19時11分20秒(G.M.T.)の地震は,マグニチュード81/2におよぶ最大級のものであって,チリ中部地方に大きな被害を生じたばかりでなく,それによつて生じた津波は,太平洋各地,ことに日本の太平洋岸に大きな被害をもたらしたことは周知の通りである。
1960年5月21日以降1960年12月までに,チリ地域に起った地震を,U．S．C.G.S.の報告(Preliminary Determination of Epicenters of United States Coast and Geodetic Survey)から拾って第2表に掲げる。主なものについては,東京大学地震研究所筑波山支所における発現時刻,同所および気象庁松代地震観測所で決められたマグニチュードを併記してある。それ以前のチリ地域の地震活動をみるために,同じくU.S.C.G.S.の報告から,1960年1月以降5月20日までの地震を拾つて掲げた。第1図には第2表に掲げられた地震の震央が示してある。
表および図からわかるように・5月21日に始まった地震活動は,チリ中部から南部にかけて分布しているが,10月下旬より北部でも地震活動が活発になり,そのうちの最大のものは,マグニチュード7を越えている。これらはいちおう別のグループと考えられるので,表では()を付してある。時間的な経過を追うためには,5月21日一6月24日の間を1日ごとに,5月一12月の間を1旬ごとに分けて,消長を示したのが第2図と第3図である。チリ北部の地震は,第3図では○で示してある。マグニチュードはPasadenaとBerkeleyの値に基いて示されている。
5月22日19時11分20秒の最大の地震を本震と考えれば,約33時間前より活発な前震活動があり,そのうち四つはマグニチュード7を越えている。余震活動も活発で,5月以前の状態と比較するとき,1961年に入つてもまだ続いているとみられる。
前震は,37(1/2)^oS,73(1/2)^ oW付近の狭い地域に集中しているが,余震は本震のあとだんだん地域が拡がって,南北1,000km以上におよんでいる。本震の位置は,はじめ38^oS,73(1/2)^oWと発表されたが,のちに41^oS,73(1/2)^oWと訂正された。
第4図,第5図,第6図に本震を含む記象を掲げてある。本震は非常に大きかったことと,3個の地震(マグニチュード7^3/4,7(1/2)〜7(3/4),8(1/2))が重なっていることとのため,その記象の解読は極めて困難である。参照のため,25日18時34分33秒の余震(マグニチュード6(1/2)〜6(3/4))の記象を第7図に掲げた。本震余震に共通して,SS相の少しあとの部分で振巾が著しく大きく,特に水平動では最大振巾を与えていることが特微である。

Seismological Data of Chilean Earthquakes in 1960

Earthquakes occurred in Chile during theperiod from 21 May to 31 December, 1960, were abridged frow the Preliminary Determination of Epicenters of United States Coastand Geodetic Survey (the Yellow Card) and listed in Table 2. For greater shocks, their arrival times at Tsukuba Seismological Observatory,the Earthquake Research Institute, University of Tokyo, and their magnitudes determined by this station and the Matsushiro
Seismological Observatory, Japan Meteorological Agency, were listed, too. To scope the seismic activity in Chile during this period, earthquakes in and near Chile which occurred during the period from January to 20 May, 1960 were abridged from the Yellow Card and listed in Table 1. Fig. 1 shows the epicentral distribution of the earthquakes. listed in Table 2.
As shown in Table 2 and Fig. 1, the seismic activity was originated in central and southern parts of Chile after 21 May, 1960, while another activity took place in northern Chile after the end of October of that year. Shocks. belonging to the latter one are parenthesized, in Table 2 and indicated by a white circle in Fig. 3. Some of these shocks had a magnitude exceeding 7.
To clarify time series, the frequency of earthquakes occurred every day from 21 May to 24 June and the frequency of earthquakes occurred every ten days from May to De- cember, 1960, were shown in Fig. 2 and Fig. 3, respectively.
The magnitudes of these earthquakes determined at Pasadena and Berkeley, were also indicated in the figures.
If we regard the greatest shock that occurred at 19h llm 20s GMT, 22 May, 1960, as a main shock, we may say that a violent foreshock sctivity began about thirty three hours preceding the main shock. Four of the foreshocks had the magnitudes more than 7.
The aftershock activity was very remarkable and seems to had been continuing in 1961. The foreshocks in the biginning were concentrated around the position, 37(1/2)^o S, 73(1/2)^o W, but the epicentral distribution was spread gradually southwards and it ranged the distance over 1,000 kilometers. The epicenter of the main shock was first reported as 38^o S., 73(1/2)^o W by U. S. C. G. S., but later revised into 41^o S., 73(1/2)^o W.
Figs. 4, 5, 6 and 7 show the seismograms including the main shock recorded at Mt. Tsukuba and at Hongo, Tokyo.
The main shock was very large and its earthquake motion was superposed on two large fore-shocks (M=7(3/4) and 7(1/2)-7(3/4)), so that the seismogram is too much complicated to be interpreted.
For reference, the seismogram of an aftershock (M:6(1/2)-6(3/4) ) of 08 h 34 m 33 s, 25 May, 1960, was shown in Fig. 8.
As common feature, both the main and the after shocks had very large amplitudes in the part after the SS phase, and especially in the horizontal components, that part gave a maximum amplitude.

地図 Fig. 1. Epicentral distribution of earthquakes in Chile during the period from 21 May to 31 December, 1961.

表 Table 1. Earthquakes in and near Chile during the period from January, 1960 to 20 May, 1960.

写真 Table 2. Earthquakes in Chile during the period from 21 May to 31 December, 1960. (Abridged from Preliminary Determination of Epicenters, U. S. C. G. S.)

表 Table 2.

地図 Fig. 2. Numbers of earthquakes occurred every day in Ghile during the period from 21 May to 24 June, 1960.

地図 Fig. 3. Numbers of earthquakes occurred every ten days in Chile during the period from May to December, 1960.

地図 Fig. 4. Chilean earthquakes (including the main shock) recorded by Columbia Long Period Seismographs at Mt. Tsukuba.

地図 Fig. 5. Chilean earthquakes (the main shock) recorded by Anderson-Wood Torsion Seismograph at Mt. Tsukuba. Magnifications are those on the microfilm reader ( x 8).

地図 Fig. 6. Chilean earthquakes (including the main shock) recorded by the seismograph HES 1-20 at Mt. Tsukuba. Magnifrcatiori are these on micro film reader (x8),

地図 Fig. 7. Chilean earthquakes (an aftershock) recorded by Columbia Long Period Seismographs at Mt. Tsukuba. Instrumental constants are the same to those of Fig. 4.

地図 Fig. 8. Chilean earthquake (the main shock) recorded by the Omori Seismograph in Tokyo.

Drawing of Refraction Diagrams and Analysis of the Chilian Tsunami of May 22, 1960 on a Terrestrial Globe

Abstract

Refraction diagrams of the Chilian Tsunami of May 22, 196Q are directly drawn on a terrestrial globe. The arrival time of the frontal waves is, grosso modo, in agreement with that obtained from the records of the tide-gauges installated over the Pacific Ocean. Because of simplicity and accuracy, our new method is highly recommended.

1. Introduction

In general, anything drawn on a spherical surface can not be projected on a plane chart without deformation. On constructing on a plane chart refraction diagram of a great tsunami, such as the Chilian Tsunami of of May 22, 1960, travelling over a very long distance, it is troublesome to take into ac- count this deformation depending on the latitude or the longitude. So we make use of the terrestrial globe of 75 cm in diameter, of our Institute, to construct refraction diagrams of the Chilian Tsunami. Owing to simplicity, it must be certainly one of the most accurate and recommendable methods.

2. Method

(1) Contours are drawn every five hundred meters on the following bathymetric charts published by the Japanese Hydrographic Office
No. 838, Pacific Ocean-Northern Portion (1941) 1:17,500,000 (Lat. 0ー)
No. 806, South Pacific Ocean-Central portion (1938) 1:6,900,000 (Lat. 0ー)
No. 808, South Pacific Ocean-Eastern portion (1938) 1:8,070,000 (Lat. 19ー)
No. 813, South Pacific Ocean-South-Western Portion (1938) 1:6,016,000 (Lat. 45ー)
No. 814, South Pacific Ocean-South-Eastern Portion (1938) 1:6,036,000 (Lat. 45ー)
No. 830, South Pacific Ocean-North-Western Portion (1938) 1:6,900,000 (Lat. 0ー)
The drawing of the contours being more or less subject to the individual variations of the drawer, everyone of the authors takes a part of this work upon himself in the case 1 and only H. Sudo occupies himself about it in the cases 2a and 2b.
(2) Afraid of making dirty this big terrestrial globe which is not usually available in Japan, we cover a part of it-Pacific Ocean and its surroundings, enclosed with the two meridians of 120ーE and of 70ーW-, with 17 pieces of white paper scissored in spindle shape and then transcribe on this paper the contours prepared in (1).
(3) We superpose on it another set of 17 pieces of tracing-paper to construct a refracion diagram.
(4) We draw fronts of the tsunami, on the basis of Heugens principle, at intervals of the distance travelled for half an hour, supposing that the origin is situated at 37ーS, 74ーW in the case 1 and at 41ーS, 73.5ーW in the cases 2a and 2b, although the latter is found inland and that the depth is uniformly 2,000m around the originto drawthe first circular front. The distanced travelled by one step of half an hour is given by the formula d=1800 x (gH)^(1/2) (in meters) where H is the depth and g the acceleration of gravity, supposed to be 9.80 m/sec. Here again, on account of the individual variations, each one takes a part of the drawing upon himself in the case 1, K. Takano alone in the case 2a and Y. Nagata alone in the case 2b.
(4) Whenever appears the criss-cross, we cut off the waves behind the frontal wave, for it is in the arrival time of the front that we are particularly interested in this study. The figures 1, 2a and 2b represent the refraction diagrams which we obtain in this way, corresponding to the cases l, 2a and 2b.

表 Table. Travel times of the frontal waves obtained from our diagrams and the tide-gauge records

地図 Fig. 1. Refraction diagram of the Tsunami originated in 37^oS, 74^oW

地図 Fig, 2a. Refraction diagrams of the Tsunami originated in 41ーS, 73.5ーW, drawn by K. Takano. Dashed lines represent great circles passing on the origin.

地図 Fig. 2b. Refraction diagram of the Tsunami originated in 41ーS, 73.5ーW drawn by Y. Nagata,

3. Discussion

The table tabulates the travel times obtained from our diagrams and from the record of the tide-gauges at various points in and around the Pacific Ocean. We refer mainly to the Report of the U. S. Coast and Geodetic Survey(1) and to the Report of the Japan Meteorological Agency(2).
Of no importance is the discrepancy between the travel time obtained in the case 2a and that obtained in the case 2b. Its maximum value is only 1.5%. The individual variations are not very significant in the drawing of wave fronts on a chart if it is already contoured.
Along the eastern and northern coasts of the Pacific Ocean, the travel time obtained from the tide-gauges falls between the two travel times obtained in the cases 2a and 2b. Of course, the discrepancy between the case 1 and the cases 2a,2b increases according as the tide station is nearer to the origin. The result obtained in the case 1 is in better agreement with that obtained from the tidegauges along the coast of the South America. Generally speaking, longer the distance from the origin, smaller the effect of the am- biguity of its position. Along the coast of Japan, the result obtained in the cases 2a and 2b is in better agreement with that obtained from the records of the tide-gauges, and in the Mid Pacific Ocean it is the result obtained in the case 1 that shows a better accordance.
The discrepancy is singularly remakable at the Pago Pago, the Eniwetok, and the Moen. The front of the Tsunami arrives at the stations of those islands much earlier than the arrival time expected from the refraction diagrams. For the moment, we have no any explanation of it.
By the drawing of great circles passing on the origin, as shown in the figure 2a one sees the wave energy has a tendency to concentrate in the neighbourhood of Japan. If the depth were constant throughout the Pacific Ocean, the wave front would travel always perpendicularly to those great circles. It is perhaps needless to take the irregular topography of the bottom into consideration, if one is concerned only in a rough prediction of the arrival time at the coast of Japan and in explaining qualitatively that the height of a tsunami caused off Chili is, as a first approximation, higher there than at other- coasts of the Pacific Ocean.
The discrepancy between the records of the tide-gauges and our result may be principally attributed to the following:
(1) The soundings are not sufficiently available in the Pacific Ocean, especially in the Southern Pacific.
(2) Our method is not competent to discuss the distribution of the wave energy. If the energy of the frontal wave is very weak, its arrival can not be always detected in the record of the tidegauge.
(3) It is difficult to precisely determine from our refraction diagrams the travel time at the coast without making use of more detailed charts.
(4) The position of the origin is ambiguous. The origin of the Tsunami is certainly not a point but a somewhat extended domain.
(5) In addition, it is not necessarily obvious that the wave velocity is equal to ,gH^1/2 , Of some importance are the force of Coriolis, the permeability of bottom sediments and the friction between the sea and the atmosphere on the one hand, between the sea and the bottom on the other hand.