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Prediction of Tokai Earthquake — SCIENCE & TECHNOLOGY TRENDS 3 Gap Between Research and Implementation — Prediction of Tokai Earthquake — SHOZO MAT S U M URA Affiliated Fellow concerned, it without doubt falls into the category 1 Introduction of “implementation of earthquake prediction.” So what is the current situation of “research and In the early morning of August 11, 2009, an implementation of Tokai earthquake prediction?” earthquake with magnitude of 6.5 occurred in As shown in Table 1, diverse organizations are Suruga Bay, shaking such cities as Omaezaki and involved in Tokai earthquake prediction in their Yaizu with an intensity of 6 or lower. Since the respective fields. Among them, the one that is threat of a “Tokai earthquake” had been touted for actually engaged in earthquake prediction is the more than 30 years in Shizuoka Prefecture, many Earthquake Assessment Committee for the Areas people in the prefecture thought that “it (the quake) Under Intensified Measures Against Earthquake was finally here.” Shortly afterward, however, Disaster (hereinafter referred to as EAC), which was they learned that it was not a Tokai earthquake established within the Japan Meteorological Agency after all, but were still concerned that the tremor in 1979. On the other hand, the Coordinating may have been a precursor to a Tokai earthquake. Committee for Earthquake Prediction, which was This is a legitimate concern. However, earthquake established in 1969, is a forum for researchers at researchers have so far been unable to produce any universities and national research institutes. As satisfactory answers. can be seen from the fact that the predecessor of In any field of science, in order to spread research the EAC was the Tokai Earthquake Assessment results to society and see them reflected in real life, Committee (Tokai EAC), which was established in other words, in order for research results to be put within the Coordinating Committee for Earthquake into practice, there are several steps that have to be Prediction, there was no major separation between followed, such as ascertaining the effectiveness of “research” and “implementation” of Tokai the research results and preparing a manual. This is earthquake prediction. However, due to a series why there is always a certain discrepancy between of unforeseen events observed in the last ten research and implementation. It may be difficult to years or so, the Tokai earthquake has prompted bridge the discrepancy, but if research advances, unexpected topics of discussion. Researchers’ implementation is expected to progress along with perception of the Tokai earthquake is no longer it. simple. However, it is not advisable to change the In the field of earthquake prediction, however, earthquake prediction system every time a new such a scenario cannot be expected. There have been view or idea about Tokai earthquakes is published. no successful examples of earthquake prediction This is because the research and implementation of and therefore it would be questionable to discuss earthquake prediction, which had originally been the “implementation” of earthquake prediction. viewed from the same perspective, have gradually Generally speaking, it is extremely difficult to begun to lose touch with each other and can no predict earthquakes. In previous reports, I already longer be measured by the same yardstick. Under explained that there are no examples of earthquake such circumstances, earthquake prediction is not prediction backed by scientific verification. accurately communicated to the local communities However, as far as “Tokai earthquake prediction” is likely to be affected by earthquakes. 36 QUARTERLY REVIEW No.35 /April 2010 Table 1 : Organization and Supervisory Authority Involved in Tokai Earthquake Prediction and Their Main Role Organization Supervisory Authority Main Role Central Disaster Prevention Council Cabinet office Estimation of damage Earthquake Assessment Committee for Areas Under Intensified Measures Japan Meteorological Agency Imminent prediction Against Earthquake Disaster (EAC) Coordinating Committee for Examination of observation and Geographical Survey Institute Earthquake Prediction analysis results Headquarters for Earthquake MEXT (Ministry of Education, Culture, Current assessment/Long-term Research Promotion Sports, Science and Technology) forecast Seismological Society of Japan Incorporated body Research in general Prepared by the STFC The purpose of this article is to renew the Peninsula and Cape Muroto but “contracted” in the perception of Tokai earthquake prediction held by Sea of Enshu (reversed arrow in Figure 1). Mogi the researchers involved, by shedding light on the interpreted this to mean that the strain that had gap between research and implementation, and, at remained compressed in the former three areas was the same time, express our hope and expectations released due to the occurrence of the Great Kanto for their further efforts. As a starter, the background Earthquake of 1923, the Tonankai Earthquake of leading up to the establishment of the EAC will be 1944 and the Nankai Earthquake of 1946, but that reviewed in Chapter 2. Then, arguments for and an assumed earthquake had yet to occur in the Sea against Tokai earthquake theories will be introduced of Enshu. Although Mogi’s interpretation was rough in Chapter 3, newly-discovered events and compared with GPS-based observations, it was phenomenon in Chapter 4, and various inferences in persuasive and easy to understand. Chapter 5. Finally, in Chapter 6, this author would Following Mogi’s article, Ishibashi compared the like to express his opinions about the attitudes of source area of the Ansei-Tokai Earthquake of 1854 the researchers involved in earthquake prediction by with that of the Showa Earthquake of 1944 and citing the incidents of the researchers’ earthquake found that, in the case of the latter, the asperities warnings that caused turmoil in the early 2000s. had yet to be ruptured in and around Suruga Bay. Based on this, Ishibashi proposed a hypothesis 2 Evolution of Research and that the strain in the area had yet to be released Implementation of Earthquake and remained critical. Attaching importance to the Prediction Ishibashi theory, the Central Disaster Prevention Council in 1978 set up an assumed source area 2-1 Start of earthquake prediction system of a Tokai earthquake (rectangled area in Figure It was the “Suruga Bay Earthquake Theory”,[2] 3) in line with the Ishibashi theory and enacted which was announced by Katsuhiko Ishibashi at the “the Special Measures Law for Countermeasures meeting of the Seismological Society of Japan in the Against Large Earthquakes,” i.e., a Tokai autumn of 1976, that first prompted people to talk earthquake countermeasures law. Prompted by the about a Tokai earthquake. However, Ishibashi was establishment of the law, the Japan Meteorological not the first to point out the possibility of a great Agency inaugurated the EAC, establishing an earthquake hitting the Tokai region. In 1970, Kiyoo earthquake prediction system as a national strategy. Mogi pointed out in his article[3] the possibility The basis of prediction was the anomalous slope of a great earthquake in the Sea of Enshu. Figure change shortly before the Tonankai Earthquake of 1 shows the patterns of strain in the northern 1944, which was excavated by Mogi (1984).[4] (Figure edge of the Philippine Sea Plate, analyzed by the 2: The day before this earthquake, an unexpected Geographical Survey Institute from differences in change in inclination was observed in measurements the measurements conducted during the Meiji era of the water level around Kakegawa.) The change (1883-1904) and Showa era (1948-1964). It shows was interpreted as a pre-slip that occurred shortly that the strain “expanded” in Sagami Bay, Kii before the Tonankai Earthquake. This idea still 37 1 圧縮歪が解消 2 されていたの 3 に対し、遠州灘 4 では起きるべ SCIENCE & TECHNOLOGY TRENDS 5 き地震がまだ 6 起きていない、 7 と解釈したの Strain of the Japanese Archipelago The difference between the measurement in the Meiji1 8圧 縮で歪あがる解。G消PS 観 Era (1883–1904) and the measurement in the Showa Era2 9さ れ測てのい発た達のした (1948–1964) 3 10に 対今しか、遠ら州見灘れば 4 11で は粗起いき観る測べに基 5 12き 地づ震いがてまいだたも 6 13起 きのてのい、なこいの、解釈 7 14と 解は釈分しかたりの易く 図表 2 測地測量による日本列島 60 年間のひずみ 8 15で あ説る得。力GPSが観あっ 参考文献 3) を基に科学技術動向研究センターにて作成 9 16測 のた発。達 した 17 これに続いて石橋は、遠州灘に起きる地震の繰り返し10と 思わ今れかたら1見854れ年ば安政 18 東海地震と 1944 年昭和東南海地震の震源域を比較し、後11者 で粗はい駿河観湾測周に辺基が割 19 れ残っており、結果としてこの部分の歪がMogi臨 (1970)界状態のま12ま にづあるい、てといいたうも仮説 20 を提唱した。この説を重大視した当時の中央防災会議は13、 197の8 の年、、こ石の橋解説釈に準 21 14 は分かり易く 図表じ2Figure た測東地 海1測 :地 量Measurement震によ想る定日震本 of源列 60域島 Yearsを60設 年of定 Strain間しの（ひ of図 ずtheみ表 Japanese 4 の長 Archipelago方形枠）、また、東海地震対策法 22 15 [3] 説得力があっ とも言うべ参き考「文大献規3) 模を地基震に科対学Prepared策技特術別動 by措向 the置研 STFC究法セ」 basedンをタ制ー on定に Referenceしてた作成。 これをきっかけとし 23 て、気象庁に判定会が発足し、名実ともに国家戦略とし16て のた地。震 予知実践体制 17 これに続いて石橋は、遠州灘に起きる地震の繰り返しと思わ24れ たが1ス854タ年ー安ト政した。 18 東海地震と 1944 年昭和東南海地震の震源域を比較し、後者で25は 駿河湾予周知辺のが根割拠と 19 れ残っており、結果としてこの部分の歪が臨界状態のままに26あ る、さとれいたうの仮は説、こ 20 を提唱した。この説を重大視した当時の中央防災会議は、197278 年、れ石橋も説に茂準 木 21 じた東海地震想定震源域を設定し（図表 4 の長方形枠）、また28、 東海(1地98震4)対4) 策に法よ っ 22 とも言うべき「大規模地震対策特別措置法」を制定した。こ29れ をきてっ発か掘けさとしれ た 23 て、気象庁に判定会が発足し、名実ともに国家戦略としての30地 震予19知44実年践東体南制海地 24 31が ス震タ直ー前トのし異た常。 傾 25 32 予斜知変の化根拠でとあ る 26 33さ れ（た図の表は3、掛こ川市 27 34れ 近もくの茂水準木測量 Figure図表 32 : 東Abnormal南海地 震Crustal直前 にChanges静岡県 Observed掛川市付 Shortly近で観 Before測され theた Tonankai異常地殻 Earthquake傾斜 4) Around Kakegawa, Shizuoka Prefecture 28 35( 198区4)間でに地よ震っ前日 4) [4] 出典Source:：参考 29Reference文 献36て 発か掘ら急さ激れなた傾斜 30 1944 年東南海地 forms the pillar of the Tokai
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