著者

山科 健一郎

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.44, no.2, pp.71-82, 1999

参考文献数

79

被引用文献数

1

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Associated with the 1914 great eruption at Sakurajima volcano, southwestern Japan, the maximum height of volcanic cloud is discussed based on collected documents, sketches and photographs in those days. A series of photographs up to around 10 : 40 on January 12 (in Japanese Standard Time) represents that the volcanic cloud height attained to 7,000 to 8,000 m above sea level. After then, it proved that several documents reported the height to be 9,500-15,000 m, or even more than 18,000 m a.s.l, although it is difficult to obtain reliable evidences. Considering these reports and other observations from a distance, the height of 15,000 m is tentatively proposed here as a possible maximum value. According to an empirical relation, an eruption rate of small pyroclastic materials is suggested as, roughly speaking, 5,000 tons per second or 20 millions of tons per hour, if the volcanic cloud was 15,000 m in height.

著者

山科 健一郎

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.43, no.5, pp.385-401, 1998-10-30

被引用文献数

2

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Various suggestive documents and associated sketehes are collected for understanding the pre-eruptive and the earliest stages of the 1914 great eruption of Sakurajima volcano, southwestern Japan, in Taisho era. Based on these records, the premonitory process to the eruption was reviewed especially with respect to the occurrence of many earthquakes which resulted in repeated rock falls with dust clouds, unusual upwelling of water and hot spring, and emission of volcanic smoke in the morning of January 12. Although there are many descriptions on the beginning of the remarkable eruption, they are sometimes inconsistent with each other. In the present paper, it is proposed that the valcano started to erupt around 09 : 58 on January 12 (Japanese Standard Time) at 200 m in height in the western slope of the mountain. In several minutes, a line of craterlets was formed between 200-500 m in height in the WNW-ESE direction. The development of a subsurface fissure in this direction resulted in another outbreak in the southeastern slope probably around 10 : 05. For the better understanding of this important eruptive event, discoveries of additional references are still desired.

著者

山科 健一郎 村井 勇

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.50, no.3, pp.295-302, 1976-03-31

著者

山科 健一郎 村井 勇

出版者

東京大学地震研究所

雑誌

東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.50, no.3, pp.295-302, 1976-03-31

著者

山科 健一郎

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.58, no.1, pp.103-114, 2013-03-29

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桜島火山の噴火活動について見通しを得るため,北部鹿児島湾とほぼ位置が重なる姶良カルデラの周りの地殻変動について,特に水準点2474番と2480番の相対的な高さの変化に注目して検討を加えた.この区間では,これまで注目されることがほとんどなかったが,1914年の桜島火山の大きな噴火に先立って明瞭な膨張が生じていたであろうことが確かめられた.これにより,大きな噴火に先立って姶良カルデラ地下に蓄えられたマグマの1914年時点の限界量が推測される.1914年の噴火によって姶良カルデラでは顕著な収縮が生じたが,その後膨張が進んで1900年(大噴火まで14年)の水準を超え,1970年代初め頃には1914年の限界値にかなり近づいたと考えられる.桜島では,1970年代から80年代にかけて爆発的活動が活発に続いた.この期間,姶良カルデラの膨張は停滞およびやや後退していたが,桜島の爆発的な活動が低下すると再び変動が進み始めた.近年,ここで推測された1914年の限界値にさらに近づきつつあり,大きな噴火の可能性があり得ることを示している.一方,姶良カルデラ地下のマグマ量の増減と桜島からの噴出物量の収支については課題があり,今後の検討に委ねられる.

著者

山岡 耕春 井田 喜明 山科 健一郎 渡辺 秀文

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集 (ISSN:04534360)

巻号頁・発行日

vol.34, no.4, pp.263-274, 1989

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Mt. Mihara of Izu-Oshima Volcano exploded on November 16, 1987 after one year's rest of its eruptivity. The eruption followed an intensive activity of earthquakes at the summit which began in January 1987. We studied the earthquakes and their mechanisms with a closely installed seismograph network around the summit. We found that most of the earthquakes occurred very narrow portion just below the summit crater with radius of 300 m. Their focal depths are shallower than 100 m above sea level. Most of the focal mechanisms are of normal types. The seismic activity ceased after this event. These facts show that the earthquakes were caused by small break of the bottom of the crater which was filled with the lava of the 1986 eruption, probably due to the load of the lava. The event on November 16 was the final break of the bottom which supported the load of the lava above it. The explosion on November 16 was caused by the sudden fall of both the bottom and the lava above it. The pressurized gas in the cavity below the bottom moved explosively upward in exchange of the falling body.

著者

山科 健一郎

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.44, no.2, pp.71-82, 1999-04-30 (Released:2017-03-20)

参考文献数

79

被引用文献数

2

---

Associated with the 1914 great eruption at Sakurajima volcano, southwestern Japan, the maximum height of volcanic cloud is discussed based on collected documents, sketches and photographs in those days. A series of photographs up to around 10 : 40 on January 12 (in Japanese Standard Time) represents that the volcanic cloud height attained to 7,000 to 8,000 m above sea level. After then, it proved that several documents reported the height to be 9,500-15,000 m, or even more than 18,000 m a.s.l, although it is difficult to obtain reliable evidences. Considering these reports and other observations from a distance, the height of 15,000 m is tentatively proposed here as a possible maximum value. According to an empirical relation, an eruption rate of small pyroclastic materials is suggested as, roughly speaking, 5,000 tons per second or 20 millions of tons per hour, if the volcanic cloud was 15,000 m in height.

著者

山科 健一郎

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.43, no.5, pp.385-401, 1998-10-30 (Released:2017-03-20)

参考文献数

69

被引用文献数

2

---

Various suggestive documents and associated sketehes are collected for understanding the pre-eruptive and the earliest stages of the 1914 great eruption of Sakurajima volcano, southwestern Japan, in Taisho era. Based on these records, the premonitory process to the eruption was reviewed especially with respect to the occurrence of many earthquakes which resulted in repeated rock falls with dust clouds, unusual upwelling of water and hot spring, and emission of volcanic smoke in the morning of January 12. Although there are many descriptions on the beginning of the remarkable eruption, they are sometimes inconsistent with each other. In the present paper, it is proposed that the valcano started to erupt around 09 : 58 on January 12 (Japanese Standard Time) at 200 m in height in the western slope of the mountain. In several minutes, a line of craterlets was formed between 200-500 m in height in the WNW-ESE direction. The development of a subsurface fissure in this direction resulted in another outbreak in the southeastern slope probably around 10 : 05. For the better understanding of this important eruptive event, discoveries of additional references are still desired.

著者

山科 健一郎

出版者

東京大学

雑誌

東京大學地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.75, no.1, pp.79-91, 2000

被引用文献数

2

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In order to find a practical method to assess forthcoming activity of aftershocks, an attempt was made to predict a plausible range of the number of major aftershocks of the 1999 Chi-Chi, Taiwan earthquake of September 20 (UTC;Ms=7.7). Although a method of predicting the probability of aftershocks had been proposed, assuming that parameters in the modified Omori formula would not change during the period of prediction, such an assumption might sometimes be invalid at the time of the especially large aftershocks. For this reason, a range of the number of aftershocks was experimentally discussed between September 22 and November 21 based on the 5-95% or the 0-90% points of the Poisson distribution. As a result, 11 cases were successful among 13 trials, suggesting that a prediction of the range of the number of aftershocks will be available for practical use, at least to some extent.1999年9月20日(世界時)に発生した台湾集集地震について,想定した期間にある大きさ以上の余震が何回起こるか,試験的な予測を試みた.予測が当たる確率を上げるためには適当な幅を考える必要があるが,ここでは90%くらいの確度を想定して,ポアソン分布の5%および95%点を予測数の上下限の幅として考えた.ただし,下限値が0に減少したときには,ポアソン分布の0~90%点をとれば十分かもしれない.また,期待値が5以下のときはその1/2~2倍くらい,期待値が20~30のときはその1/1.5~1.5倍くらいの範囲をとると,ある程度近似できる(その際,下限値を求めるときは小数点以下を切り捨てる).観測された余震のデータを改良大森公式にあてはめてその係数を定めれば,任意の期間に起こる余震数の期待値を求めることができる.これをもとに予測回数の幅を推測するが,期待値に誤差が見込まれるときは,それに応じて予測の幅を広げる必要が生じる.今回の台湾の余震活動では, 9月22日~11月21日までの2ヵ月間,初めは1日ごと,その後は1週間ごとにマグニチュード5.0以上の余震数を予測した.合計13回の予測の結果をみると, 11回が予測幅の範囲内に収まり, 2回が予測幅をそれぞれ一つ超過した.地震発生直後に入手できる地震データは不完全な場合が多く,具体的に予測の作業を行うときは,それによる不確かさも考慮しなければならない.このような難しさもあるが,今回の試行では, 85%程度の成功率を得た.どのくらい活発な余震活動がこれから先に見込まれるか,本稿のような方法によってある程度の目安が得られれば,それなりに役に立つのではないかと思われる.なお,期待値が与えられたときに,ポアソン分布の5~95%幅が具体的にどのような値をとるかを表の形で表し,また,参考までにその値を算出する近似式を示した.

著者

山科 健一郎 中村 一明 福留 高明 佐藤 魂夫 田中 和夫

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.38, no.1, pp.81-91, 1985-03-25 (Released:2010-03-11)

参考文献数

18

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Based on a few tens of photographs, height change of Kyuroku-shima Island, which locates very close to the focal region of the Japan Sea earthquake (M=7.7) on May 26th, 1983, is analyzed. 1) The island and adjacent small islets are considered to have subsided by about 30-40cm associated with the 1983 earthquake. The average offset obtained by 13 reliable photographs is 32±9cm. 2) Precursory deformation and secular change of the height were not found during 1964 through 1982. No detectable deformation was caused by largest aftershock (M=7.1) on June 21, 1983, and other aftershock activity. 3) Coseismic tilt and local collapse were not observed in the island. 4) In some cases, a height can be inferred even from snapshots with the error less than several percents. Crustal uplift and subsidence more than 10-20cm may be possible to be detected photographically at the seashore and lakeside.

著者

山科 健一郎

出版者

特定非営利活動法人日本火山学会

雑誌

日本火山学会講演予稿集

巻号頁・発行日

vol.1988, no.1, 1988-07-16

著者

山科 健一郎 松島 健

出版者

特定非営利活動法人日本火山学会

雑誌

日本火山学会講演予稿集

巻号頁・発行日

vol.1994, no.2, 1994-10-20

著者

山科 健一郎 高橋 正義

出版者

東京大学地震研究所

雑誌

東京大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.58, no.3, pp.655-666, 1984-01-14

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1982年5月に伊豆半島北東部の川奈崎付近で起きた群発地震活動(M=2.0)について,現地で臨時観測を行った.観測期間は活動の最盛期を過ぎた5月12~14日で,2観測点は固定し,他の1観測点を次々に移動する方式をとった.川奈崎付近に集中して発生した一群の地震(ここではa型と呼ぶ)があり,計5ケ所のP時刻から平均的な震源の位置と観測点補正を求めた.今回のような移動多点観測も,ある場合には役に立つものと思われる.一方,川奈崎付近の活動は5月13日の朝に急速に低下したが,ちょうどその前に,約30km南方で群発活動が起きている.活動の低下はまずa型の地震群に現われ,数時間遅れて周辺も静かになった.A tail of the swarm activity (M=2.0) near Kawana-zaki in the northeastern part of the Izu Peninsula in May, 1982, was observed by a temporary microseismic network installed close to the epicentral region. During the observations on May 12-14th, two seismometers were fixed at the respective places and another was moved from place to place. Station corrections and the average location of the events which occurred within a small area near Kawana-zaki (they are called "a-type" in this paper) were obtained from P arrivals of the two fixed and three tentative stations, suggesting the utility of the moving installation of instruments in some cases. The observation also shows a distinct decrease in activity near Kawana-zaki in the morning of May 13th, following the earthquake swarm which occurred about 30km to the south. The decrease in activity occurred at fast in the hypocentral region of the a-type events, and in the adjacent areas several hours later.