著者
高山 博之 吉田 明夫
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.57, no.4, pp.409-418, 2005-03-20 (Released:2010-03-11)
参考文献数
12

When a larger earthquake than the preceding ones occurs successively in a clustered activity, it seems a further larger earthquake is apt to be observed afterwards (Yoshikawa et al., 2000). We investigate alarm rate, success rate, and probability gain for the occurrence of an earthquake with M5 or larger in such sequential activities. We use the JMA catalogue during the period from 1995 to 2000. First, we select out clusters of shallow (depth≤30km) earthquakes withM≥2.5 in and around Japanese islands. We name the first earthquake in a cluster E0, and the one larger than E0 that occurs first in the succeeding activity E1, and term such clusters that contain E1 earthquake E1-class clusters. E2 earthquake and E2-class clusters are defined in the similar way. We calculate the alarm rate, the success rate and the probability gain, when M≥5 earthquakes are forecasted using E1-class clusters and E2-class clusters, respectively. We also examine how the alarm and success rates change when criterion of selecting clusters and upper limit of distance and time interval are varied. It is shown that, for E1-class clusters, the alarm rate is 24 to 30% and the success rate is about 5%. For E2-class clusters, the alarm rate is 10 to 15% and the success rate is 10 to 14%, and we get a value as large as 5702.2 for the probability gain in the best case that both the criterion and the upper limit of selecting clusters are set to be 5km-5days. The large values of the alarm and success rates and the probability gain indicate that the algorithm for forecasting M5 earthquakes proposed in this paper is practically effective as well as statistically significant.
著者
吉田 明夫 高山 博之 細野 耕司
出版者
日本水文科学会
雑誌
日本水文科学会誌 (ISSN:13429612)
巻号頁・発行日
vol.43, no.4, pp.111-117, 2013-11-30 (Released:2014-01-16)
参考文献数
7

紀伊半島から四国にかけて東西に走る中央構造線の南側ゾーンの地震発生層は異常に浅い。ここで“異常に”と言ったのは,一般に地形高度と地殻内の地震発生層の深さとの間には,標高が高いほど浅くなるという相関関係が認められるが,このゾーンには和歌山平野や徳島平野等の低地が存在するにもかかわらず,火山フロント沿いの山地の地震発生層と同じくらいに浅いということを表わしている。地震発生層の下限の深さは,地殻物質が脆性から粘弾性に変わる温度によって規定されていると考えると,地震発生層が浅いということは地殻内の温度が相対的に高くなっていることを示す。なぜ,中央構造線の南側のゾーンは高温になっているのか。これについては,同ゾーン内の和歌山の群発活動域において熱水の上昇が推定されていることを参考にすると,そこには地下深部から高温の流体が上昇していることが考えられる。
著者
吉田 明夫
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.103, no.3, pp.201-206, 1994-06-25 (Released:2009-11-12)
参考文献数
17
被引用文献数
1

Correlation between earthquakes in Kanto region and intermediate-depth earthquakes in Hida region, central Japan is re-investigated. We found that a significant correlation exists between earthquakes with depth of 70 km and deeper in western Kanto and intermediate-depth earthquakes in Hida region, but such a correlation is not seen for earthquakes in eastern Kanto. This result shows that earthquakes occurring in the Pacific slab are well correlated each other, but earthquakes which occur in relation to the subduction of the Philippine Sea plate are not correlated with intermediate-depth earthquakes in the Pacific plate. Intermediate-depth earthquakes in Hida region have a tendency to precede earthquakes in western Kanto. This feature may be related to the dynamics of the plate motion which oceanic plate is pulled by the subducted slab.
著者
吉田 明夫 青木 元
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.111, no.2, pp.212-221, 2002-04-25 (Released:2009-11-12)
参考文献数
26
被引用文献数
2

We show that conspicuous seismic quiescence occurred in large areas along the coast of the Japan Sea before the 1891 Nobi, 1964 Niigata, 1983 Central Japan Sea, and 2000 Western Tottori Prefecture Earthquake. If we had noticed the quiescence that had appeared since the late 1980s along the northern coasts of Shimane, Tottori, and Hyogo Prefectures and had remembered the feature that a large earthquake in the coastal region of the Japan Sea is likely to be preceded by a widely extended seismic quiescence along the coast, we could have paid close attention to the focal region of the Western Tottori Prefecture Earthquake. We think the occurrence of seismic quiescence in a large area before a large earthquake implies that the preparatory process proceeds not only in the focal region, but in the circumferential areas as well.
著者
吉田 明夫
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.103, no.3, pp.201-206, 1994-06-25
被引用文献数
1 1

Correlation between earthquakes in Kanto region and intermediate-depth earthquakes in Hida region, central Japan is re-investigated. We found that a significant correlation exists between earthquakes with depth of 70 km and deeper in western Kanto and intermediate-depth earthquakes in Hida region, but such a correlation is not seen for earthquakes in eastern Kanto. This result shows that earthquakes occurring in the Pacific slab are well correlated each other, but earthquakes which occur in relation to the subduction of the Philippine Sea plate are not correlated with intermediate-depth earthquakes in the Pacific plate. Intermediate-depth earthquakes in Hida region have a tendency to precede earthquakes in western Kanto. This feature may be related to the dynamics of the plate motion which oceanic plate is pulled by the subducted slab.
著者
吉田 明夫 青木 元
出版者
公益社団法人 東京地学協会
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.111, no.2, pp.212-221, 2002-04-25
参考文献数
26
被引用文献数
1 2

We show that conspicuous seismic quiescence occurred in large areas along the coast of the Japan Sea before the 1891 Nobi, 1964 Niigata, 1983 Central Japan Sea, and 2000 Western Tottori Prefecture Earthquake. If we had noticed the quiescence that had appeared since the late 1980s along the northern coasts of Shimane, Tottori, and Hyogo Prefectures and had remembered the feature that a large earthquake in the coastal region of the Japan Sea is likely to be preceded by a widely extended seismic quiescence along the coast, we could have paid close attention to the focal region of the Western Tottori Prefecture Earthquake. We think the occurrence of seismic quiescence in a large area before a large earthquake implies that the preparatory process proceeds not only in the focal region, but in the circumferential areas as well.
著者
金谷 整一 中村 克典 秋庭 満輝 寺川 眞理 池亀 寛治 長野 広美 浦辺 菜穂子 浦辺 誠 大山 末広 小柳 剛 長野 大樹 野口 悦士 手塚 賢至 手塚 田津子 川上 哲也 木下 大然 斉藤 俊浩 吉田 明夫 吉村 充史 吉村 加代子 平山 未来 山口 恵美 稲本 龍生 穴井 隆文 坂本 法博 古市 康廣
出版者
日本生態学会
雑誌
保全生態学研究 = Japanese journal of conservation ecology (ISSN:13424327)
巻号頁・発行日
vol.10, no.1, pp.77-84, 2005-06-30
参考文献数
24
被引用文献数
3

2003年9月に種子島の木成国有林で確認されたヤクタネゴヨウの新群生地において, 2004年1月に調査を行った結果, ヤクタネゴヨウ13個体とクロマツ7個体の枯死が確認された.これらのうち, 材片を採取したヤクタネゴヨウ10個体のうち7個体からと, クロマツ7個体のうち6個体からマツ材線虫病の病原体であるマツノザイセンチュウが検出された.このまま枯死したヤクタネゴヨウとクロマツを放置すると, 今後, マツ材線虫病被害が拡大すると予測されることから, すべての枯死木を伐倒し約50cmの丸太に玉切りし, 直径1cm以上の枝とともに個体群外へ搬出した.搬出した丸太と枝は, 焼物製作のための薪として焼却した.今回の活動を踏まえ, 今後のヤクタネゴヨウ自生地保全にむけたマツ材線虫病被害木のモニタリングから処理の一連の作業手順を提案した.
著者
吉田 明夫 高山 博之
出版者
Tokyo Geographical Society
雑誌
地學雜誌 (ISSN:0022135X)
巻号頁・発行日
vol.103, no.6, pp.696-705, 1994-12-10
参考文献数
12
被引用文献数
1 1

We show that seismic activity decreased clearly in a wide area before the 1953 Boso-oki earthquake and the 1972 Hechijojima-toho-oki earthquake. In both cases the seismic quiescence extended to the Tokyo Metropolitan area. Marking precursory activity appeared several years before the Boso-oki earthquake in the Chiba prefecture and in the sea region off-Ibaraki prefecture. It is also noted that the seismicity in the Kanto region as well as in the sea region south off-Boso Peninsula decreased conspicuously after the Boso-oki earthquake. On the contrary an increase of the seismicity was observed after the Hachijojima-toho-oki earthquake, although deep seismic activities decreased remarkably. We show that seismic quiescences preceding the Boso-oki earthquake and the Hachijojima-toho-oki earthquake were detectable before their occurrences, and no other statistically significant quiescence has appeared in the south off-Kanto region since 1926. It is proposed that the occurrence of a large earthquake may be predicted by monitoring changes of the seismicity in a wide area.
著者
楠城 一嘉 吉田 明夫
出版者
日本地球惑星科学連合
雑誌
JpGU-AGU Joint Meeting 2017
巻号頁・発行日
2017-03-10

各マグニチュードの地震発生頻度を、横軸にマグニチュード(M)、縦軸に頻度の対数をとってプロットすると、十分に検知できているマグニチュードの範囲で、地震頻度分布は直線で良く近似できる。グーテンベルグ-リヒターの法則として知られているこの分布式で、直線の傾きの値(b値)は、地震発生域の差応力の大きさと相関がみられることが知られており、一般に、断層のアスペリティのような応力の集中しているところではb値は小さく、一方、差応力が小さいところ、例えば、間隙水圧が大きなところ等では、b値は大きい。こうした経験的知識を基に、2011年東北地方太平洋沖地震の震源域のb値の空間分布の変化を調べたTormann et al. (2015)は、2013年以降、b値の空間分布が、ほぼ震源域全体に渡って東北地方太平洋沖地震発生前のb値の分布に戻っているという結果を得たことから、東北地方太平洋沖地震の震源域の応力場は、わずか数年で地震発生前の状況に回復したとみなし、このことから、巨大地震は特徴的な再来周期を持たず、時間的にランダムに発生すると結論している。これは本当だろうか?もし、彼らの結果、及びその推論が正しければ、これまで文部科学省の地震調査委員会が進めてきた地震発生の長期予測の考え方を根本的に見直す必要が生じることになる。 我々は、こうした問題意識を持って、東北地方太平洋沖海域におけるb値の時間的変化を詳細に解析した。Tormann et al. (2015)の解析方法と基本的には同じだが、プレート境界での地震と上盤の地震を分けたこと、地震活動度の空間分布の時間的な変化について考慮したことなど、いくつかの点で、手法に改善を加えた。 我々の解析で得た主要な結果は以下の通りである。2011年東北地方太平洋沖地震で大きくすべった領域では、b値は地震直前の小さな値(Nanjo et al., 2012)に戻っていない。牡鹿半島沖合の想定宮城県沖地震の震源域付近でもM9地震の前にb値が次第に小さくなっていた。三陸北部沖合の海域ではb値の小さい状態が継続しており、しかも最近、低b値域の範囲が西側に広がってきている様子が見える。この低b値域の北部は1994年三陸はるか沖地震の破壊開始域と重なるが、南部は過去の大地震の破壊域と重ならない。総じて、我々の結果では、Tormann et al. (2015)が主張するように震源域全体でb値は東北地方太平洋沖地震前の状況に戻ったとは言えない。また、三陸北部沖合の低b値域では、近い将来における大地震発生の可能性も考慮して注意深く推移を見守っていく必要があると考える。
著者
原田 昌武 細野 耕司 小林 昭夫 行竹 洋平 吉田 明夫
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.55, no.4, pp.193-199, 2010-08-31
被引用文献数
1

Temporal changes in dilatational strain and the activity of low-frequency earthquakes around Mt. Fuji and Hakone volcano are investigated. It is shown that both cumulative strain and cumulative number of low-frequency earthquakes around Mt. Fuji have been increasing since the end of 2006. The tendency is more notable for relatively larger earthquakes rather than smaller earthquakes. The b value for earthquakes during the period after November 2006 is significantly smaller than the b value during the period from January 2004 through October 2006. These facts suggest that the crustal stress surrounding the source region of low-frequancy earthquakes has been increasing. We think this is the cause of the dilatational strain observed around Mt. Fuji. On the other hand, a clear relationship is not seen between extensional strain events observed three times since 2001 and the activity in low-frequancy earthquakes around Hakone volcano.
著者
吉田 明夫 瀬野 徹三
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.37, no.6, pp.297-301, 1992-12-25
被引用文献数
4
著者
吉田 明夫 古屋 逸夫
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.45, no.1, pp.71-82, 1992-03-24 (Released:2010-03-11)
参考文献数
24
被引用文献数
1 1

Pattern of occurrence of precursory phenomena differs significantly in various respects for each earthquake. It is not the same even for earthquakes occurring in adjacent areas. Amplitude of precursory change is not necessarily large at nearer sites, and that it is very often larger than that of coseismic change. These features suggest that precursors occur locally at weak points or stress concentrating sites. It seems that desrimination of earthquake precursors from noises which are not directly related to the occurrence of earthquake is intrinsically difficult. Whether some observed change is a precursor or not may be expressed in a probabilistic way. When various kinds of anomalous change are observed at the same time, the possibility that they are true precursors will be increased. It is important to elucidate the occurrence mechanism of precursors in relation with structure and its change of seismogenic field.
著者
細野 耕司 西 政樹 吉田 明夫
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.59, no.1, pp.29-37, 2006-08-31 (Released:2013-08-05)
参考文献数
22

We investigated changes in the depth distribution of aftershocks of three large inland earthquakes in Japan, the 2000 western Tottori Prefecture Earthquake of M 7.3, the 2003 northern Miyagi Prefecture earthquake of M 6.4, and the 2004 mid Niigata Prefecture earthquake of M 6.8. For all of them we found that the seismogenic layer extended to the deeper and shallower zones after occurrence of the main shock. The shallow and deep activities decayed faster than the activity in the intermediate depth. This suggests that when stress is built up very fast, brittle fractures can occur in the zone where increase of stress is usually relaxed through a ductile process. Our results also show that a fault motion could extend to the outside of the seismogenic zone estimated from the background seismicity, which should be taken into consideration in the hazard assessment.
著者
吉田 明夫 高山 博之
出版者
公益社団法人 東京地学協会
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.103, no.6, pp.696-705, 1994-12-10 (Released:2009-11-12)
参考文献数
13
被引用文献数
1 1

We show that seismic activity decreased clearly in a wide area before the 1953 Boso-oki earthquake and the 1972 Hechijojima-toho-oki earthquake. In both cases the seismic quiescence extended to the Tokyo Metropolitan area. Marking precursory activity appeared several years before the Boso-oki earthquake in the Chiba prefecture and in the sea region off-Ibaraki prefecture. It is also noted that the seismicity in the Kanto region as well as in the sea region south off-Boso Peninsula decreased conspicuously after the Boso-oki earthquake. On the contrary an increase of the seismicity was observed after the Hachijojima-toho-oki earthquake, although deep seismic activities decreased remarkably. We show that seismic quiescences preceding the Boso-oki earthquake and the Hachijojima-toho-oki earthquake were detectable before their occurrences, and no other statistically significant quiescence has appeared in the south off-Kanto region since 1926. It is proposed that the occurrence of a large earthquake may be predicted by monitoring changes of the seismicity in a wide area.
著者
吉田 明夫 伊藤 秀美 細野 耕司
出版者
公益社団法人 東京地学協会
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.105, no.1, pp.77-87, 1996-02-25 (Released:2009-11-12)
参考文献数
22
被引用文献数
2 2

Several examples are presented which seismic quiescence appeared in a wide area around the foci of intraplate earthquakes before their occurrence. A noteworthy feature is that the quiescence area extends along tectonic zones over more than several times of the focal region of the main shock. This phenomenon suggests that stress in a wide area along tectonic zones changes before the occurrence of major intraplate earthquake. We consider that the stress change is a manifestation of a significant physical process leading to earthquake occurrence. An apparently puzzling fact which earthquake precursors are sometimes observed at distant places from the focal region in the specific direction may be explained by such stress change. Further, it is expected that the precursory seismic quiescence provides us with a promising clue to the short-term prediction of intraplate earthquake.
著者
草野 富二雄 吉田 明夫
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.43, no.4, pp.459-469, 1990-12-24 (Released:2010-03-11)
参考文献数
20

Aftershock activity of the 1987 Chiba-ken Toho-oki earthquake (M6.7) is investigated using JMA data. It is found that aftershocks during two weeks just after the main shock occurred mostly in a region to the east side of the fault plane which is nearly north-south direction with a steep dip to the east. However, aftershock activity in the area to the west side of the fault plane became high since the beginning of January 1988. The contrast between spatial distribution of aftershocks in December 1987 and that after January 1988 is conspicuous. The later activity was concentrated to a rather small area and the largest aftershock occurred on 16 January in the active region. The mechanism of the largest aftershock was reverse type in contrast to the mechanism of the main shock which was strike slip type. Further, pattern of temporal decrease of aftershock activity deviated notably from the Omori's formula when the later activity was started. All these characteristics suggest that most earthquakes which occurred in the region to the west of the fault plane of the main shock after January 1988 are not the so-called aftershocks in a narrow sense, but that they represent an appearance of a new fracture, which occurrence might be caused by the stress concentration due to the fault motion of the main shock. The phenomenon that aftershock activity in the either one side against a fault plane is higher than that in the other side is frequently observed, even for fault motions of strike slip type. It is interesting to note that seismicity before the main shock was also asymmetrical, i. e. it was active in the region to the west of the fault plane of the 1987 earthquake. The seismicity in the recent one year also seems to be active in the west region. These features may show that the western block to the fault plane has taken a positive part in the accumulation process of stress in the focal region of the 1987 Chiba-ken Toho-oki earthquake.
著者
小林 昭夫 吉田 明夫
出版者
日本測地学会
雑誌
測地学会誌 (ISSN:00380830)
巻号頁・発行日
vol.50, no.1, pp.39-42, 2004-03-25 (Released:2010-09-07)
参考文献数
11

We investigated crustal deformation after the 1946 Nankai earthquake using tide gauge records. Although resolution of tide gauge records is not so high for seeing the temporal change in detail, vertical crustal movements whose relaxation times are between several months to years can be detected by them. It was reported that there had been a postseismic crustal deformation with a time constant of 4-5 months in southern Kui Peninsula (Kobayashi et al., 2002). In this paper we show that crustal deformations with a longer relaxation time of a few years were observed in northern Shikoku, examining tide gauge records at such stations as Takamatsu, Sumoto and Kobe. These observations suggest that there was a time lag in the development of postseismic slip between shallow and deeper parts on the plate interface after the Nankai earthquake.
著者
小林 昭夫 真砂 礼宏 吉田 明夫
出版者
日本測地学会
雑誌
測地学会誌 (ISSN:00380830)
巻号頁・発行日
vol.48, no.1, pp.1-12, 2002-03-25 (Released:2011-03-01)
参考文献数
28
被引用文献数
1

We examined tide gauge records at stations in and around the Kui peninsula to find if a precursory crustal deformation occurred before the 1946 Nankai earthquake. First, we removed effects of atmospheric pressure and astronomical tide on the records. Then, we tried to get rid of the effects of the oceanic current by taking the difference of the records betweentwo stations. After these corrections we found that sea level at Uragami where is located on the southeastern coast of the Kui peninsula had risen about 10 cm just before the Nankai earthquake. The sea level change, if we consider that to represent real subsidence of land near Uragami, could be explained by supposing that a slow fault slip corresponding to moment magnitude 6.9 occurred on the plate boundary in the offing of southeast of the Kui peninsula near the hypocenter of the Nankai earthquake.