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

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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 細野 耕司

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.47, no.6, pp.727-738, 2003-01-08 (Released:2017-03-20)

参考文献数

28

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We investigated how the intermediate-depth seismicity changes with depth in the Pacific slab beneath Hokhaido and the Kanto district using JMA data since Oct. 1997. We found that seismicity in the upper seismic plane decreases noticeably at about the depth of 100 km and on its deeper side both in Hokkaido and the Kanto district. In Hokkaido the volcanic front is located nearly above the line where the seismicity in the upper seismic plane starts to decrease (the D line). This feature is the same as that seen in the Tohoku district (Hosono and Yoshida, 200la). In the Kanto region, however, the D line is located several tens km to the east of the volcanic front, the cause of which may be attributed to the subduction of the Philippine Sea plate above the Pacific plate. We think the noticeable decrease of seismicity in the upper seismic plane at about the depth of 100 km which is commonly observed in the Pacific slab beneath Japan and the correspondence between the location of the D Iine and the volcanic front in Hokkaido and the Tohoku district indicate that the decrease of seismicity in the upper seismic plane may be related to the genetic process of magmatic bodies in the subduction zone.

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

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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 外谷 健 吉田 真希子

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.113, no.1, pp.107-124, 2004-02-25 (Released:2009-11-12)

参考文献数

39

被引用文献数

1 1

---

We investigated solar-cycle and semiannual variations of magnetic storms based on data observed at the Kakioka Magnetic Observatory since 1924. First, we show that magnetic storms with a peak value of ≥ 100 nT are considered to have been almost completely recorded for both types of storm, i.e., those with sudden commencement (Ssc) and those with gradual commencement (Sg). Using data for storms larger than 100 nT, we found that the variation of numbers of Ssc correlates well with that of the sunspot Wolf numbers, but that of Sg does not. The number of storms decreases linearly with the peak value in the semi-logarithmic plot. The inclination is steeper for Sg storms than for Ssc storms. The semiannual variation, that is, more storms are observed in spring and fall than in summer and winter, is clearly seen for storms with a peak value ≥ 100 nT for Sg, but it is recognized only for larger storms with a peak value ≥. 150 nT for Ssc. Concordant with the difference between Ssc and Sg in the semiannual variation, the decrease in the number of large storms in the semi-logarithmic plot is less in spring and fall than that in summer and winter for Ssc. Although such a difference is not apparently seen for Sg, the ratio of the number of storms with a peak value ≥ 150 nT to that of storms with a peak value between 100 nT and 150 nT is larger for spring and fall. We propose the hypothesis that the efficiency of magnetic reconnection depends on the three dimensional direction of the magnetic field in the solar wind relative to the geomagnetic field, and on the north-south symmetry of the geomagnetosphere when it is seen from the stream of the solar wind. We think these “equinoctial effects” are the main causes of the semiannual variation in the number of large magnetic storms. As for the Sudden Commencement (SC), the semiannual variation is not seen, but an annual variation with the number of SC being larger in summer is observed. The reason may be that the shock wave in the solar wind hits against the northern part of the geomagnetosphere in summer, and the southern part in winter.

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

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.104, no.6, pp.801-808, 1995-12-10 (Released:2009-11-12)

参考文献数

10

---

Correlation between seismic activities in the focal region of the Hyogo-ken Nanbu earthquake and in the surrounding regions were investigated. We found that seismic activity in the Tanba region had been well correlated with that of the Wakayama region, but the correlation has disappeared in 1990s. Activity to the west of Tanba region shows a tendency to be delayed to the activity in the Tanba region and this tendency is concordant with the f eature shown by Yoshida and Takayama (1992) that activity in the Mino region is advanced a few years against the activities in the Tanba and Wakayama regions. Such seismic correlations with time lags between surrounding areas of the Kinki triangle are considered to mean that tectonic stress in that district has a tendency to propagate or diffuse to the west at the velocity of 10 km/year. We present some evidence which decrease of the seismicity in the Tanba region in 1992-1993 period and increase in 1994 might be precursory changes for the Hyogoken Nanbu earthquake. Just after the Hyogo-ken Nanbu earthquake seismic activity in the Tanba region increased remarkably and an activity of small earthquakes was observed near the Yamasaki fault located to the west of the Hyogo-ken Nanbu earthquake. However, no unusual change of seismicity was seen in the Wakayama active region. Because a disastrous intraplate earthquake is likely to be followed by another large earthquake, and the most probable site of the succeeding large earthquake is the place where seismicity becomes active after the first earthquake (Yoshida and Ito, 1995), the Tanba region and its surrounding areas should be watched intensively in the following several to ten years.

著者

吉田 明夫

出版者

気象庁気象研究所

雑誌

Papers in Meteorology and Geophysics (ISSN:0031126X)

巻号頁・発行日

vol.41, no.1, pp.15-32, 1990 (Released:2006-10-20)

参考文献数

35

被引用文献数

2 5

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日本列島とその周辺に発生した浅い大地震 (M≥5, 深さ≤30km) の前震活動の特徴を調べた。1961年から1988年までの期間に発生した110個の本震の中、41個、すなわち37%が前震を伴っていた。ここで定義した前震とは、本震の前30日以内に、本震の震央を中心として20′×20′の領域内に発生した地震をいう。前震がみられた地震の割合は、期間を40日とし、また範囲を30′×30′に拡げてもほとんど変わらない。前震時系列の中の最後の前震は、本震発生前1日以内に、その本震の震央のすぐ近くで発生する場合がほとんどである。1981年以後の期間をとると、前震は55%の地震について観測された。これに対して、1961-1970年の期間では前震を伴った本震の割合は27%、また1971-1980年の期間ではそれは37%である。このことは、近年、気象庁の地震検知力が格段に増大したことを示している。前震活動には著しい地域性が存在する。その注目すべき特徴の一つは、伊豆地域と九州中部に発生する地震には前震が伴いやすいことである。特に、伊豆地域では67%の地震に前震がみられた。他の地域では、この割合は26%である。更に、伊豆地域と九州に発生する地震には、しばしば群発的な前震活動が観測される。他の地域では前震を伴ったとしても、通常は1個ないし2~3個の地震が発生するのみである。なお、伊豆地域にみられる群発的な前震活動では、本震発生の2~3時間前に静穏化が生じることが多い。この現象は、大地震の発生直前に破壊の核が生成されて、震源域における応力が緩和することを示しているものと考えられる。この研究で明らかにされた前震活動の地域的な特徴は、1926年から1961年までの期間に日本とその周辺海域に発生した大・中地震の前震を調査したMogi (1963) の結果と調和的である。この事実は、Mogi (1963) も指摘しているように、これらの特徴が一時的なものではなく、その地域地域毎の地殻構造や応力の集中過程を反映した固有の性質であることを示している。前震の時系列は4つのタイプに分類することができる。タイプ1は、1個ないし2~3個の地震が本震の数日から数10日前に発生するものである。このタイプの前震中には本震の発生と直接関係しないものも含まれている可能性がある。タイプ2もタイプ1と同じように1個ないし2~3個の前震がみられる場合であるが、しかし、これらの前震は本震の直前 (通常数分以内) に発生する。このタイプの前震の発生は、本震発生に引き続く破壊の開始を表わしているのかもしれない。タイプ3の典型的な場合は、M4程度の中規模の地震が本震の数時間から1日ほど前に発生してその地震に伴う余震、時には、前震もみられるものである。この中規模の地震に伴う地震活動は、通常、本震発生の2~3時間前には静かになる。タイプ4は群発的な前震活動に対応する。タイプ3とタイプ4の前震活動の発生は、伊豆地域、フォッサ・マグナ地域、九州の中央部にほとんど限られる。これらのタイプの前震活動で、特に伊豆地域においてしばしば見られる本震発生の2~3時間前に生じる静穏化は、大きな地震の直前の予知に有効な前兆現象と考えられる。

著者

升田 吉雄 吉田 明夫 林 文明 佐々木 健 本田 良行

出版者

THE PHYSIOLOGICAL SOCIETY OF JAPAN

雑誌

The Japanese Journal of Physiology (ISSN:0021521X)

巻号頁・発行日

vol.32, no.3, pp.327-336, 1982 (Released:2011-06-07)

参考文献数

25

被引用文献数

14 19

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The steady-state ventilatory responses to hypercapnia and hypoxia in 7 assisted breath-hold divers (Funado) were compared with those in 7 normal sedentary controls.Ventilatory response to hypercapnia was measured from the slope of the hyperoxic VN-PETCO2 line, where VN was normalized minute ventilation using the allometric coefficient and PETCO2 end-tidal PCO2. The slope of this line in the Funado (1.48±0.54 liters·min-1·Torr-1) was significantly less than in the control (2.70±1.08 liters·min-1·Torr-1)(p<0.025). On the other hand, hypoxic sensitivity estimated by hyperbolic and exponential mathematical equations was not found to be significantly different between the two groups, although estimated increments in ventilation using the hyperbolic equation exhibited significantly lower response in the Funado than in the control only when PETO2 decreased lower than 50 Torr (p<0.05).These findings in the Funado were different from our previous observations obtained in unassisted breath-hold divers (Kachido), in whom no obvious attenuations in CO2sensitivity were seen. This difference was assumed to be derived from more hypercapnic and hypoxic conditions produced in the Funado than in the Kachido during diving activities.

著者

升田 吉雄 吉田 明夫 林 文明 佐々木 健 本田 良行

出版者

THE PHYSIOLOGICAL SOCIETY OF JAPAN

雑誌

The Japanese Journal of Physiology (ISSN:0021521X)

巻号頁・発行日

vol.31, no.2, pp.187-197, 1981 (Released:2011-06-07)

参考文献数

21

被引用文献数

22 26

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The ventilatory responses to hypoxia and hypercapnia of 5 Amas (Kachido) were compared with those of 5 controls of similar ages, physical characteristics and lung volumes. The responses to hypoxia and hypercapnia were analyzed by the equations originally proposed [a] by Lloyd et al. and [b] by Kronenberg et al. as follows:[a] VN=(PCO2-B')·D·(1+A/PO2-C) +VB'.[b] VN=(PCO2-B')·D·(1+R0·exp (-k·PO2)) +VB'.The CO2-response slope in hyperoxia, D, of the Ama (1.820±0.441 liters·min-1·Torr-1) was slightly higher than that of the control (1.148±0.586 liters·min-1·Torr-1), but the difference was not significant. However, the slope of CO2-response in hypoxia at PETO2=44 Torr, S44, was almost the same in the two groups (Ama, 1.822±0.689 liters·min-1·Torr-1; control, 1.742±0.902 liters·min-1·Torr-1). The ratio of S44 to D was significantly lower (p<0.05) in the Ama (1.039±0.377) than in the control (1.529±0.249). Comparing the hypoxic response in terms of the ventilation ratio (VR), the elevation of ventilation with augmentation of hypoxia in the Ama was exceeded by that in the control.Thus, it was suggested that the difference in the ventilatory response to hypoxia between the Ama (Kachido) and the control may have been derived from the respiratory adaptation of the Ama (Kachido) acquired by their daily diving activities.

著者

本田 良行 林 文明 吉田 明夫 升田 吉雄 佐々木 健

出版者

THE PHYSIOLOGICAL SOCIETY OF JAPAN

雑誌

The Japanese Journal of Physiology (ISSN:0021521X)

巻号頁・発行日

vol.31, no.2, pp.181-186, 1981 (Released:2011-06-07)

参考文献数

15

被引用文献数

3 5

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Relative contributions of chemical and non-chemical respiratory stimulations to breath-holding time (BHT) were examined in assisted (Funado) and unassisted (Kachido) breath-hold divers (Ama). In the Funado the magnitude of the chemical contribution was reduced, though statistically not significant. On the other hand, in the Kachido no difference in chemical contribution was seen from the control. This was considered to be due to the fact that ventilatory response to CO2 was reduced in the Funado, but not in the Kachido. Despite the decreased contribution of CO2 drive to BHT, absolute BHT in the Funado was not prolonged. This may be related to sensitization of the respiratory centers to non-chemical stimulation. Such adaptation would be effective for preventing the danger of losing consciousness in the Funado who face extreme hypoxia on returning to the surface from a dive.

著者

吉田 明夫 小林 昭夫 塚越 利光

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.58, no.4, pp.401-406, 2006-03-31 (Released:2010-03-11)

参考文献数

23

被引用文献数

1

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Areal strain increased noticeably in the region around the northern boundary of the Izu Peninsula in September to December 2000 when a lot of low-frequency earthquakes occurred beneath Mt. Fuji. In the same time the seismic activity in eastern Yamanashi Prefecture became low. Since increase of the areal strain indicates reduction of the pushing force of the colliding Izu block, the decrease of seismicity in eastern Yamanashi Prefecture is easily understood. Further, because diminution of the tectonic stress beneath Mt. Fuji implies reduction of the confining pressure in the magma reservoir, we think it is probable that degassing took place in the magma to build up high pressure in the focal region near the chamber which caused the remarkable activity of the low-frequency earthquakes. We suggest the noticeable increase of the areal strain in late 2000 might be produced by a mechanical separation of the Izu block from the Philippine Sea plate or detachment of the crust of the Izu block as proposed by Seno (2005).

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

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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

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

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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

吉田 明夫 ヨシダ アキオ Akio YOSHIDA

雑誌

application/pdf

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

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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