気象研究所技術報告第 69 号噴火準備期における伊豆大島の相対精密重力測定

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気象研究所技術報告第69 号 2013

53－

1.4 噴火準備期における伊豆大島の相対精密重力測定

52 気象研究所技術報告　第69 号　2013 53 気象研究所技術報告　第69 号　2013

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1㧚ߪߓ߼ߦ

㊀ജ᷹ⷰߦࠃߞߡἫጊᵴേߦ઻߁ᄌൻ߇ᝒ߃ࠄࠇߚ ߣ޿߁ႎ๔ߪޔ଀߃߫ࠛ࠻࠽ޔࡑ࡛ࡦޔਃቛፉߥߤᢙ ᄙ ޿㧔 ጊ ᧄ࡮ ઁ, 1998; ฎ ደ࡮ ઁ, 2001; Jentzsch et al., 2001; ᄢፉ࡮他, 2003; Jousset et al., 2003; Carbone et al.,

2007 ╬㧕ޕ࿾⴫ߦ߅ߌࠆ㊀ജᄌൻߪޔ࿾ਅߩኒᐲ᭴ㅧ ߩᄌൻ߿⾰㊂ߩ⒖േߦ઻ߞߡ↢ߓࠆޕߎߩߚ߼ྃἫᵴ േߦ઻߁ࡑࠣࡑߩ⒖േ߿ᄢⷙᮨߥ᭴ㅧᄌൻ߇↢ߓߚ႐ วޔ࿾⴫ߢߪ㊀ജᄌൻ߇᷹ⷰߐࠇࠆ႐ว߇޽ࠆޕ਄ㅀ ߩ㊀ജᄌൻߩႎ๔଀ߩᄙߊߪޔྃἫᵴേ೨ᓟߦ᷹ⷰߐ ࠇߡ޿ࠆޕߒ߆ߒྃἫᵴേᦼࠍߪߐ߻ྃἫḰ஻ᦼߦߪ 㗼⪺ߥ㊀ജᄌൻߪ᷹ⷰߐࠇߥ޿߽ߩߩޔἫጊ૕⋥ਅߢ ࡑࠣࡑߩ⫾Ⓧ߇ⴕࠊࠇߡ޿ࠆ႐วߦߪޔ࿾ਅߩኒᐲ᭴ ㅧߪࠊߕ߆ߥ߇ࠄᄌൻߔࠆߚ߼ޔ♖ኒߥ㊀ജ᷹ቯࠍ⛮ ⛯ߔࠇ߫ߎࠇࠍᬌ⍮ߢ߈ࠆߪߕߢ޽ࠆޕ દ⼺ᄢፉἫጊߪ20 ਎♿એ㒠ߎࠇ߹ߢ⚂ 30 ᐕ㑆㓒ߢ

ྃἫḰ஻ᦼߦ߅ߌࠆદ⼺ᄢፉߩ⋧ኻ♖ኒ㊀ജ᷹ቯ

㜞ᧁᦶల_{࡮⑔੗ᢘ৻࡮ጊ㉿ޓᐔ㧔᳇⽎⎇ⓥᚲ࿾㔡Ἣጊ⎇ⓥㇱ㧕} ޓޓޓ ⮮ේஜᴦ_{㧔ᄢ㒋▤඙᳇⽎บ㧕} ടᴦደ⑺ታ_{㧔ᄢፉ᷹୥ᚲ㧕} ޓ_{⃻ᚲዻ㧦ᢥㇱ⑼ቇ⋭⎇ⓥ㐿⊒ዪ࿾㔡࡮㒐ἴ⎇ⓥ⺖} _{⃻ᚲዻ㧦᳇⽎ᐡ࿾㔡ἫጊㇱἫጊ⺖ ޓޓޓޓޓޓޓ}

Relative Precise Gravity Survey at Izu-Oshima Volcano in the Eruption Preparation Period

by

Akimichi Takagi1*_{, Keiichi Fukui}1_{, Hitoshi Yamasato}1_{, Kenji Fujiwara}2**_{and Akimi Kajiya}3**

1. Seismology and Volcanology Research Department, Meteorological Research Institute, Tsukuba, Japan 2. Osaka District Meteorological Observatory, Osaka, Japan

3. Oshima Weather Station, Oshima, Tokyo, Japan

*Present afliation: Earthquake and Disaster-Reduction Research Division, Research and Development Bureau, Ministry of Education, Culture, Sports, Science and Technology, Tokyo, Japan

**Present afliation: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency, Tokyo, Japan

(Received August 7, 2009; Accepted March 5, 2010; Published September 2, 2010)

Abstract

In order to investigate the magma accumulation process of Izu-Oshima Volcano in the eruption preparation period, we conducted 14 relative microgravity surveys from 2004 to 2009. The gravity changes tend to decrease near the north-ern margin of the summit caldera, and rates of negative gravity changes reached as much as 0.015 mgal/year. Assuming the Mogi model, we estimated the pressure increase at a depth of 3.65 km with increasing volume of 7.6 × 106_m3_/year, which could account for the observed data. However, the uplift rate calculated with the estimated increasing volume would be ve times as large as the observed uplift rate by the GPS network, so these estimated parameters cannot ex-plain both gravity changes and uplift changes simultaneously.

Izu-Oshima Island could be a volcano having an extraordinary magma accumulation system that cannot be ex-pressed as a simple physical model. More accurate microgravity survey with the uplift observation should be conducted in the future to clarify the magma accumulation system of this complicated volcano.

Corresponding author: Akimichi Takagi

Earthquake and Disaster-Reduction Research Division, Research and Development Bureau, Ministry of Education, Culture, Sports, Science and Technology – Japan

E-mail: [email protected]

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A. Takagi et al. Vol. 61 2 ߶߷๟ᦼ⊛ߦྃἫᵴേࠍ➅ࠅ㄰ߒߡ߈ߚ㧔Ꮉㄝ_{, 1991} ╬㧕ޕ೨࿁1986 ᐕߩྃἫᓟ߽࿾ਅߢߪࡑࠣࡑ⫾Ⓧ߇⛮ ⛯ߒߡ޿ࠆߣ⠨߃ࠄࠇޔߎߩߎߣߪ࿾Ზᄌേ᷹ⷰ߆ࠄ ߽ቯ㊂⊛ߦ⹏ଔߐࠇߡ޿ࠆ㧔㜞ᧁ࡮ઁ, 2008㧕ޕᚒޘߪޔ ㊀ജᄌൻ߆ࠄࡑࠣࡑ⫾Ⓧㆊ⒟ࠍᬌ⍮ߔࠆ⋡⊛ߢޔ2004 ᐕ߆ࠄ♖ኒ⋧ኻ㊀ജ᷹ⷰࠍ㐿ᆎߒߚޕߎࠇ߹ߢߩ5 ᐕ 㑆ߢ14 ࿁ߩ᷹ⷰ߇ታᣉߐࠇߚߩߢޔߎߎ߹ߢߩ࠺࡯࠲ ߩߣࠅ߹ߣ߼ࠍⴕ޿ޔ᣿ࠄ߆ߦߥߞߚߎߣࠍႎ๔ߔࠆޕ 2㧚᷹ⷰ 2.1ޓ᷹ⷰὐ દ⼺ᄢፉߢߪޔ࿖࿯࿾ℂ㒮㧔GSI㧕߇৻╬㊀ജὐߣ ᳓Ḱὐࠍᢛ஻ߒޔᢙᐕߦ㧝࿁㊀ജ᷹ቯࠍታᣉߒߡ޿ࠆޕ ߹ߚ᧲੩ᄢቇ࿾㔡⎇ⓥᚲ㧔ERI㧕߽ፉౝߦ᳓Ḱὐ✂ࠍ᭴ ▽ߒߡ޿ࠆޕ1986 ᐕߩྃἫᵴേ೨ᓟߦߎࠇࠄߩ᷹ὐߢ ㊀ജ᷹ⷰ߇ታᣉߐࠇޔᄢਭ଻࡮ઁ㧔1988㧕ߪྃἫ೨ᓟ ߢᢙච㨪ࡑࠗ࠽ࠬᢙච_{μgal ߩᄌൻ߇↢ߓߚߎߣࠍႎ๔} ߒߡ޿ࠆޕ߹ߚޔ⪺⠪ߩ߭ߣࠅ߽ߎࠇࠄߩ᷹ὐߦ߅޿ ߡ೎ߦ᷹ⷰࠍⴕ޿ޔ㧙100 μgal㨪㧗 50 μgal ߩᄌൻࠍႎ ๔ߒߡ޿ࠆ㧔ዊᴰ࡮ઁ, 1988㧕ޕ ᚒޘߪޔㆊ෰ߩ᷹ⷰᚑᨐࠍෳᾖߔࠆߎߣ߇ߢ߈ࠆࠃ ߁ޔߎࠇ߹ߢߩ᷹ⷰᚑᨐߣห᭽ߦ࿖࿯࿾ℂ㒮ߩ㊀ജὐ ෸߮᳓Ḱὐޔ᧲੩ᄢቇ࿾㔡⎇ⓥᚲߩၮḰὐࠍᒁ߈⛯߈ ೑↪ߔࠆߎߣߣߒޔߎࠇߦട߃ޔ࿖࿯࿾ℂ㒮ߩ㔚ሶ ၮḰὐޔ᳇⽎ᐡ㧔JMA㧕߅ࠃ߮᳇⽎⎇ⓥᚲ㧔MRI㧕ߩ GPS ᷹ⷰὐߢߩ㊀ജ᷹߽ⷰᣂߚߦട߃ߚޕ㊀ജᄌൻ㊂ ߩㆡಾߥផቯߦߪޔ᷹ὐߦ߅޿ߡ਄ਅᄌേࠍᛠីߔࠆ ᔅⷐ߇޽ࠆ߇ޔߎࠇࠄߩὐߢߪ᳓Ḱ᷹ⷰ߿GPS ᷹ⷰߦ ࠃࠅ࿾Ზᄌേ᷹ⷰ߇ታᣉߐࠇߡ޿ࠆߚ߼ޔផቯߩߚ߼ ߩ⵬ᱜߦ೑↪߇น⢻ߢ޽ࠆޕ Fig. 1 ߦ᷹ⷰὐ㈩⟎ࠍ␜ߔޕ⊕޿ਣ㧔٤㧕ߪర↸ߩᄢ ፉ᷹୥ᚲ࿾㔡⸘ቶߩၮบߦᝪ߃ઃߌࠄࠇߚ৻╬㊀ജὐ FGS ࠍ␜ߔޕ㊀ജ᷹ቯߪߎߎࠍ࿕ቯὐߣߒߡⴕߞߚޕ 㤥⦡ߩਣ㧔٨㧕ޔ྾ⷺᒻ㧔ع㧕ޔਃⷺᒻ㧔ً㧕ߪߘࠇߙ ࠇޔ࿖࿯࿾ℂ㒮ߩ᳓Ḱὐ෸߮㔚ሶၮḰὐޔ᧲੩ᄢቇߩ ၮḰὐޔ᳇⽎⎇ⓥᚲ෸߮᳇⽎ᐡߩGPS ᷹ⷰὐࠍ␜ߔޕ 5 ᐕ㑆ߩ᷹ⷰᦼ㑆ਛߦ᷹ὐߩ੢ᄬޔ޽ࠆ޿ߪ᷹ⷰὐߩ ⒖⸳╬ߦࠃࠅ᷹ⷰࠍਛᱛ޽ࠆ޿ߪભᱛߒߚὐ߇޽ࠆޕ ߎࠇࠄߪࠪࡦࡏ࡞ߣ᷹ⷰὐฬࠍዊߐߊᮡ⸥ߒߚޕTable 1 ߦ᷹ⷰὐߩᐳᮡ╬ߩ⹦⚦ࠍ␜ߔޕߎߎߦ᷹ⷰὐ⒖⸳ ߦ઻߁᷹ⷰὐฬߩᄌᦝߦߟ޿ߡ߽⸥ߔޕ᳇⽎⎇ⓥᚲߩ GPS ᷹ⷰὐߪ➅ࠅ㄰ߒ᷹ⷰ߆ࠄㅪ⛯᷹ⷰὐߦ㗅ᰴ⒖ⴕ ߒߚߎߣߦ઻޿ޔ㊀ജ᷹ቯὐ߽8 ὐߢ⒖⸳߇ᔅⷐߣߥߞ ߚޕߎࠇߦࠃࠅਛᱛ޽ࠆ޿ߪભᱛߒߚ᷹ⷰὐฬߩᦨᓟ ߦߪᷝ߃ሼo ࠍട߃ߚޕߩߴ 51 ߩ᷹ⷰὐߢ᷹ቯࠍታᣉ ߒߚ߇ޔ⃻࿷ታᣉߒߡ޿ࠆὐߪ38 ὐߢ޽ࠆޕTable 㧝ਛޔ ᤊශࠍᷝ߃ߚ᷹ὐ߇⃻࿷ਛᱛ߹ߚߪભᱛߒߚ߽ߩߢ޽ ࠆޕ ߥ߅ޔ1986 ᐕྃἫᓟߩ 1992 ᐕߦᄢፉ᷹୥ᚲ߇ᵤ୚ ઃ߆ࠄర↸ኅߩ਄ߦ⒖⸳ߒߚߎߣߦ઻޿ޔ৻╬㊀ജὐ FGS ߽ห᭽ߦ⒖⸳ߐࠇߚޕߎࠇ߹ߢޔ⒖⸳೨ߩ FGS ࠍ ࿕ቯὐߦߒߚ᷹ⷰߦၮߠߊᄙߊߩႎ๔߇ߥߐࠇߡ޿ࠆ ߇ޔᧄႎ๔ߪ⒖⸳ᓟߩFGS ࠍ࿕ቯὐߦߒߚ߽ߩߢ޽ࠆޕ 2.2ޓ㊀ജ⸘ ㊀ജ᷹ⷰߦ߅ߌࠆ᷹ቯ♖ᐲߪޔ㊀ജ⸘ࠍหᤨߦⶄᢙ บ૶↪ߔࠆߎߣߢะ਄ߐߖࠆߎߣ߇น⢻ߢ޽ࠆޕᚒޘ ߪLaCoste & Romberg D-type #109㧔એਅޔD109㧕ޔScin-trex CG-3M #454㧔એਅޔCG3㧕ޔ෸߮ Scin#109㧔એਅޔD109㧕ޔScin-trex CG5 #033 㧔એਅޔCG5㧕ߩ 3 บߩ⋧ኻ㊀ജ⸘ࠍ૶↪ߒߚ㧔ߚߛߒ 2008 ᐕ 2 ᦬߹ߢߪ೨⠪ߩ 2 บߩߺ㧕ޕߎߩ߁ߜ D109 ߪ ⪺⠪ߩ߭ߣࠅ߇1985㨪1988 ᐕߦદ⼺ᄢፉߩ㊀ജ᷹ቯߦ ૶↪ߒߚ߽ߩߢ޽ࠆ㧔ዊᴰ࡮ઁ_{, 1988㧕ޕCG3 ෸߮ CG5} ߪࠨ࡯ࡏᯏ᭴ࠍណ↪ߒߚ⥄േ㊀ജ⸘ߢ޽ࠆޕD109 ߪ᷹ ቯಽ⸃⢻߇1 ᩴ㜞޿㧔0.1 μgal㧕߇ޔ❫⚦ߥᯏ᪾ᑼ㊀ജ ⸘ߢ޽ࠆߚ߼♖ᐲࠍ㜞߼ࠆߚ߼ߦޔขࠅᛒ޿ߦߪዊᴰ࡮ ઁ㧔1988㧕ߣ߶߷ห᭽ߦޔ᭽ޘߥ⚦ᔃߩᵈᗧࠍᛄߞߚޕ ᷹ቯߪᦼ㑆ࠍㅢߒߡ㜞ᧁ߇ⴕߞߚޕߥ߅ޔ㊀ജ࿕ቯὐ FGS ߢ࠳ࠗࡗ࡞୯ࠍ 175.0 ߦ࡝࠮࠶࠻ߒߡⴕߞߚޕ 2.3ޓ᷹ቯ ᷹ቯߪⶄᢙบߩ㊀ജ⸘ߢหᤨߦⴕߞߚޕ⥄േ㊀ജ⸘ ߩCG3 ߣ CG5 ߪ 1 ⑽ࠨࡦࡊ࡝ࡦࠣߢ 60 ࿁᷹ቯࠍ 3 ࠮࠶ ࠻㧔ฦ࠮࠶࠻ߩ㑆㓒ߪ30 ⑽㧕ታᣉߒߚޕ᷹ቯ࡞࡯࠻ߪ

Fig. 1 Distribution of the gravity stations on Izu-Oshima Island. The large open circle denotes a reference station of the microgravity survey. This station is named FGS and is a rst-order gravity station installed by the Geo-graphical Survey Institute of Japan (GSI). Solid circles denote bench marks and GPS-based control stations (GSI). Solid squares indicate bench marks installed by the Earthquake Research Institute, Tokyo University (ERI). Solid triangles denote GPS stations installed by the Meteorological Research Institute and the Japan Meteorological Agency (MRI–JMA). Topographical contour interval is 100 m.

気象研究所技術報告　第69号　2013

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FGS ࠍၮὐߣߔࠆᓔᓳ⋧ኻ᷹ቯߣߒߚޕ᷹ቯ࡞࡯࠻ߪ ፉߩᶏጯᴪ޿ߣౝ㒽ߦಽߌߡⴕߞߚޕ ᶏጯᴪ޿ߩ᷹ቯߩ߁ߜޔർጯ࡞࡯࠻ߪᄢፉ⷏ㇱߩ FGS ࠍၮὐߣߒޔਥߦᶏጯᴪ޿ࠍㅢࠆㇺ㆏ 208 ภ✢ᴪ ޿ߦጟ↰ࠍ⚻↱ߒޔᄢፉ᧲ㇱߢ᛬ࠅ㄰ߔޕධጯ࡞࡯࠻ ߽ห᭽ߦᵄᶋࠍ⚻↱ߒᄢፉ᧲ㇱߢ᛬ࠅ㄰ߔޕ᛬㄰ߒὐ ߪ᷹ⷰ㐿ᆎᒰೋ߆ࠄߒ߫ࠄߊߪ࿕ቯߐࠇߡ޿ߥ߆ߞߚ ߇ޔፉߩධ᧲ㇱߩੑሶጊ㧔_{G14㧕ߦ GPSޔ⥄േశᵄ᷹} 〒ⵝ⟎╬ߩ࿾Ზᄌേ᷹ⷰߩߚ߼ߩዪ⥢ࠍ⸳༡ߒߚߚ߼ޔ 2007 ᐕ 7 ᦬એ㒠ߪ G14 ࠍർጯ࡞࡯࠻෸߮ධጯ࡞࡯࠻ߩ ᛬㄰ߒቯὐߣߒߚޕ ౝ㒽ㇱߩ᷹ቯߪ_{FGS ࠍ⿠ὐߣߒޔㇺ㆏ 207 ภ✢ߢࠞ} ࡞࠺࡜ᄖベർㇱ߹ߢ⊓ࠅޔࠞ࡞࠺࡜ౝ෸߮ਃේጊ⚻↱ ߢᓮ␹Ἣ⨥ደߦ⥋ࠆ࡞࡯࠻ߢ޽ࠆޕㇺ㆏_{207 ภ✢ߩࠞ} ࡞࠺࡜ᄖベർㇱ߹ߢߩ⊓ጊ࡞࡯࠻ᴪ޿ߩ᷹ὐߪޔᄢਭ ଻࡮ઁ㧔_{1988㧕߿ዊᴰ࡮ઁ㧔1988㧕ߦࠃߞߡ 1986 ᐕྃ} Ἣ೨ᓟߩ᷹ⷰ⚿ᨐ߇ႎ๔ߐࠇ㊀ⷐߥ૏⟎ߠߌߦ޽ࠆ㧔଀ ߃ ߫ޔ_{O1004ޔO1003ޔONSENHOTEL ╬ 㧕ޕ ౝ 㒽 ࡞ ࡯} ࠻ߪ᷹ὐᢙ߇ᄙ޿ߣ޿߁ℂ↱߽޽ࠅޔ_{2006 ᐕ 7 ᦬એ㒠} ߪޔ⊓ጊ࡞࡯࠻ߣࠞ࡞࠺࡜࡞࡯࠻ߦಽߌߡታᣉߒߚޕ ᛬㄰ߒὐߪߣ߽ߦ_{GOJINKACHAYA ߢ޽ߞߚ߇ޔߎߎ} ߢߩ᷹ቯ߇࿎㔍ߣߥߞߚߚ߼ޔ_{2008 ᐕ 11 ᦬߆ࠄߪߎ} ߩㄭறߩ_{G07 ߦᄌᦝߒߚޕ} ߎࠇ߹ߢ_{14 ࿁ⴕߞߚ᷹ⷰߩጁᱧࠍ Table 2 ߦ␜ߔޕ}

Latitude Longitude Altitude

(deg min sec) (deg min sec) (m)

GSI-FGS 34 45 0.0 139 21 48.0 76.0 ᄢፉ᷹୥ᚲ䋮ᄢፉ৻╬㊀ജὐ䋮 GSI-GOJINKACHAYA* 34 44 16.3 139 22 48.3 557 ᓮ␹Ἣ⨥ደ GSI-10210 34 47 1.0 139 23 31.0 80.2 ጟ↰Ꮉ䈱㆏䋮ੑ╬᳓Ḱὐ GSI-10212 34 47 8.0 139 24 40.8 24.7 ᴰᵤ⑺ਯේ䋮ੑ╬᳓Ḱὐ GSI-10214* 34 45 47.0 139 26 1.0 78.6 ᴰᵤ⑔㊀䋮ੑ╬᳓Ḱὐ GSI-10217 34 44 26.1 139 26 4.4 348.7 ᴰᵤේ㊁䋮ੑ╬᳓Ḱὐ GSI-10220 34 42 32.3 139 26 11.3 321.7 Ꮕᧁ࿾૛Ꮉ䋮ੑ╬᳓Ḱὐ GSI-10224* 34 41 11.3 139 26 8.4 69.3 Ꮕᧁ࿾ᴒ䊉ᩮ䋮ੑ╬᳓Ḱὐ GSI-10226 34 41 5.5 139 24 14.5 29.5 Ꮕᧁ࿾䉯䊷䊉䊷䋮ੑ╬᳓Ḱὐ GSI-10228* 34 42 2.1 139 22 39.4 58.7 ㊁Ⴧ਄ጊ䋮ੑ╬᳓Ḱὐ GSI-10231* 34 43 48.2 139 21 14.5 13.5 ㊁Ⴧ䋮ੑ╬᳓Ḱὐ GSI-10233 34 45 28.2 139 21 28.0 40.9 ర↸㚍䈱⢛䋮ੑ╬᳓Ḱὐ GSI-93051 34 47 4.2 139 22 52.6 97.4 ጟ↰㐳ဈ䋮㔚ሶၮḰὐ䇸ᄢፉ䋱䇹 GSI-93055 34 41 12.0 139 26 0.5 75.9 Ꮕᧁ࿾ᴒ䊉ᩮ䋮㔚ሶၮḰὐ䇸ᄢፉ䋲䇹 GSI-960594 34 45 41.2 139 26 2.5 100.8 ᴰᵤᵤ⑔㊀䋮㔚ሶၮḰὐ䇸ᄢፉ䋳䇹 GSI-960595 34 44 15.4 139 21 30.9 46.9 ర↸ਅ㜞ᵢ䋮㔚ሶၮḰὐ䇸ᄢፉ䋴䇹 ERI-ONSENHOTEL 34 45 12.8 139 24 10.5 498.4 ᷷ᴰ䊖䊁䊦 ERI-O1003 34 45 27.5 139 23 39.3 440.5 ḡ႐ ERI-O1004 34 45 37.0 139 23 0.0 300.2 ᄢਣጊ ERI-MK* 34 43 44.4 139 23 27.5 672.0 ਃේጊἫญ✼ MRI-G01 34 46 54.0 139 21 18.2 19 䇸ർ䈱ጊ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪐㪆㪉䈎䉌㪞㪇㪈㫆䉕ᄌᦝ䋮 MRI-G01o* 34 46 42.9 139 21 16.0 25 䇸㘧ⴕ႐ධ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G02 34 46 28.5 139 24 9.0 224 䇸㪙㪫ὐ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪌㪆㪊䈎䉌㪞㪇㪉㫆䉕ᄌᦝ䋮 MRI-G02o* 34 46 9.9 139 24 15.5 270 䇸ጼ⾂᳓ᳰ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G03 34 45 58.7 139 22 26.9 188 䇸ᣥ᷹୥ᚲ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋨㪡㪤㪘㪀 MRI-G04 34 44 50.1 139 26 0.0 328 䇸ᅏጊ⍾Ṽ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G05 34 44 39.4 139 24 19.6 481 䇸ⵣ⍾Ṽർ᧲䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪏㪆㪎䈎䉌㪞㪇㪌㫆䉕ᄌᦝ䋮 MRI-G05o* 34 44 39.8 139 24 19.1 480 䇸ⵣ⍾Ṽർ᧲䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G07 34 44 16.7 139 22 49.7 558 䇸ᓮ␹Ἣ⨥ደ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋨㪡㪤㪘㪀 MRI-G09 34 44 21.7 139 25 12.7 439 䇸ⵣ⍾Ṽ᧲䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪏㪆㪎䈎䉌㪞㪇㪐㫆䉕ᄌᦝ䋮 MRI-G09o* 34 44 22.6 139 25 10.0 437 䇸ⵣ⍾Ṽ᧲䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G10 34 44 7.6 139 24 20.4 535 䇸ᰏᒻጊർ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G11 34 43 15.4 139 25 40.2 403 䇸Ꮕᧁ࿾ᬌ⍮✂䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G12 34 43 15.0 139 24 25.0 686 䇸⊕⍹ጊ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪏㪆㪎䈎䉌㪞㪈㪉㫆䉕ᄌᦝ䋮 MRI-G12o* 34 43 19.3 139 24 28.3 662 䇸⊕⍹ጊ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G13 34 42 27.2 139 22 52.5 180 䇸㑆ફᨋ㆏䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G14 34 42 45.3 139 24 46.4 615 䇸ੑሶጊ㪭㪦㪩㪫㪘㪚䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪎㪆㪎䈎䉌㪞㪈㪋㫆䉕ᄌᦝ䋮 MRI-G14o* 34 42 27.9 139 25 6.6 415 䇸ੑሶጊ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G15 34 42 7.9 139 22 11.9 32 䇸㊁Ⴧ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G16 34 42 8.3 139 26 35.2 37 䇸╩ፉ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G17 34 41 12.0 139 25 26.7 42 䇸Ꮕᧁ࿾䇹䋮㪞㪧㪪ㅪ⛯ὐ䋨㪡㪤㪘㪀 MRI-G18 34 44 46.5 139 23 30.8 555 䇸㎸┵䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G19 34 44 10.1 139 23 12.7 553 䇸㪘ὐ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪌㪆㪈㪇䈎䉌㪞㪈㪐㫆䉕ᄌᦝ䋮 MRI-G19o* 34 44 11.9 139 23 10.8 548 䇸⴫⍾Ṽ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G20 34 43 41.0 139 23 24.8 675 䇸ਃේ␹␠䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪐㪆㪉䈎䉌㪜㪩㪠㪄㪤㪢䉕ᄌᦝ䋮 MRI-G21 34 43 31.2 139 23 27.9 703 䇸ਃේᣂጊ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G22 34 43 27.6 139 23 45.1 702 䇸ਃේἫሹධ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G23 34 43 41.7 139 23 57.4 733 䇸೶䉧ፄ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G24 34 44 21.9 139 23 46.5 531 䇸㪙Ἣญ᧲䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G25 34 44 18.5 139 22 52.1 557 䇸ᓮ␹Ἣዷᦸบ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G26 34 47 21.9 139 23 28.8 3.3 䇸ጟ↰᷼䇹䋮㪞㪧㪪ㅪ⛯ὐ Site Note

(5)

Relative Precise Gravity Survey at Izu-Oshima Volcano in the Eruption Preparation Period 2010 3 FGS ࠍၮὐߣߔࠆᓔᓳ⋧ኻ᷹ቯߣߒߚޕ᷹ቯ࡞࡯࠻ߪ ፉߩᶏጯᴪ޿ߣౝ㒽ߦಽߌߡⴕߞߚޕ ᶏጯᴪ޿ߩ᷹ቯߩ߁ߜޔർጯ࡞࡯࠻ߪᄢፉ⷏ㇱߩ FGS ࠍၮὐߣߒޔਥߦᶏጯᴪ޿ࠍㅢࠆㇺ㆏ 208 ภ✢ᴪ ޿ߦጟ↰ࠍ⚻↱ߒޔᄢፉ᧲ㇱߢ᛬ࠅ㄰ߔޕධጯ࡞࡯࠻ ߽ห᭽ߦᵄᶋࠍ⚻↱ߒᄢፉ᧲ㇱߢ᛬ࠅ㄰ߔޕ᛬㄰ߒὐ ߪ᷹ⷰ㐿ᆎᒰೋ߆ࠄߒ߫ࠄߊߪ࿕ቯߐࠇߡ޿ߥ߆ߞߚ ߇ޔፉߩධ᧲ㇱߩੑሶጊ㧔_{G14㧕ߦ GPSޔ⥄േశᵄ᷹} 〒ⵝ⟎╬ߩ࿾Ზᄌേ᷹ⷰߩߚ߼ߩዪ⥢ࠍ⸳༡ߒߚߚ߼ޔ 2007 ᐕ 7 ᦬એ㒠ߪ G14 ࠍർጯ࡞࡯࠻෸߮ධጯ࡞࡯࠻ߩ ᛬㄰ߒቯὐߣߒߚޕ ౝ㒽ㇱߩ᷹ቯߪ_{FGS ࠍ⿠ὐߣߒޔㇺ㆏ 207 ภ✢ߢࠞ} ࡞࠺࡜ᄖベർㇱ߹ߢ⊓ࠅޔࠞ࡞࠺࡜ౝ෸߮ਃේጊ⚻↱ ߢᓮ␹Ἣ⨥ደߦ⥋ࠆ࡞࡯࠻ߢ޽ࠆޕㇺ㆏_{207 ภ✢ߩࠞ} ࡞࠺࡜ᄖベർㇱ߹ߢߩ⊓ጊ࡞࡯࠻ᴪ޿ߩ᷹ὐߪޔᄢਭ ଻࡮ઁ㧔_{1988㧕߿ዊᴰ࡮ઁ㧔1988㧕ߦࠃߞߡ 1986 ᐕྃ} Ἣ೨ᓟߩ᷹ⷰ⚿ᨐ߇ႎ๔ߐࠇ㊀ⷐߥ૏⟎ߠߌߦ޽ࠆ㧔଀ ߃ ߫ޔ_{O1004ޔO1003ޔONSENHOTEL ╬ 㧕ޕ ౝ 㒽 ࡞ ࡯} ࠻ߪ᷹ὐᢙ߇ᄙ޿ߣ޿߁ℂ↱߽޽ࠅޔ_{2006 ᐕ 7 ᦬એ㒠} ߪޔ⊓ጊ࡞࡯࠻ߣࠞ࡞࠺࡜࡞࡯࠻ߦಽߌߡታᣉߒߚޕ ᛬㄰ߒὐߪߣ߽ߦ_{GOJINKACHAYA ߢ޽ߞߚ߇ޔߎߎ} ߢߩ᷹ቯ߇࿎㔍ߣߥߞߚߚ߼ޔ_{2008 ᐕ 11 ᦬߆ࠄߪߎ} ߩㄭறߩ_{G07 ߦᄌᦝߒߚޕ} ߎࠇ߹ߢ_{14 ࿁ⴕߞߚ᷹ⷰߩጁᱧࠍ Table 2 ߦ␜ߔޕ}

Latitude Longitude Altitude

(deg min sec) (deg min sec) (m)

GSI-FGS 34 45 0.0 139 21 48.0 76.0 ᄢፉ᷹୥ᚲ䋮ᄢፉ৻╬㊀ജὐ䋮 GSI-GOJINKACHAYA* 34 44 16.3 139 22 48.3 557 ᓮ␹Ἣ⨥ደ GSI-10210 34 47 1.0 139 23 31.0 80.2 ጟ↰Ꮉ䈱㆏䋮ੑ╬᳓Ḱὐ GSI-10212 34 47 8.0 139 24 40.8 24.7 ᴰᵤ⑺ਯේ䋮ੑ╬᳓Ḱὐ GSI-10214* 34 45 47.0 139 26 1.0 78.6 ᴰᵤ⑔㊀䋮ੑ╬᳓Ḱὐ GSI-10217 34 44 26.1 139 26 4.4 348.7 ᴰᵤේ㊁䋮ੑ╬᳓Ḱὐ GSI-10220 34 42 32.3 139 26 11.3 321.7 Ꮕᧁ࿾૛Ꮉ䋮ੑ╬᳓Ḱὐ GSI-10224* 34 41 11.3 139 26 8.4 69.3 Ꮕᧁ࿾ᴒ䊉ᩮ䋮ੑ╬᳓Ḱὐ GSI-10226 34 41 5.5 139 24 14.5 29.5 Ꮕᧁ࿾䉯䊷䊉䊷䋮ੑ╬᳓Ḱὐ GSI-10228* 34 42 2.1 139 22 39.4 58.7 ㊁Ⴧ਄ጊ䋮ੑ╬᳓Ḱὐ GSI-10231* 34 43 48.2 139 21 14.5 13.5 ㊁Ⴧ䋮ੑ╬᳓Ḱὐ GSI-10233 34 45 28.2 139 21 28.0 40.9 ర↸㚍䈱⢛䋮ੑ╬᳓Ḱὐ GSI-93051 34 47 4.2 139 22 52.6 97.4 ጟ↰㐳ဈ䋮㔚ሶၮḰὐ䇸ᄢፉ䋱䇹 GSI-93055 34 41 12.0 139 26 0.5 75.9 Ꮕᧁ࿾ᴒ䊉ᩮ䋮㔚ሶၮḰὐ䇸ᄢፉ䋲䇹 GSI-960594 34 45 41.2 139 26 2.5 100.8 ᴰᵤᵤ⑔㊀䋮㔚ሶၮḰὐ䇸ᄢፉ䋳䇹 GSI-960595 34 44 15.4 139 21 30.9 46.9 ర↸ਅ㜞ᵢ䋮㔚ሶၮḰὐ䇸ᄢፉ䋴䇹 ERI-ONSENHOTEL 34 45 12.8 139 24 10.5 498.4 ᷷ᴰ䊖䊁䊦 ERI-O1003 34 45 27.5 139 23 39.3 440.5 ḡ႐ ERI-O1004 34 45 37.0 139 23 0.0 300.2 ᄢਣጊ ERI-MK* 34 43 44.4 139 23 27.5 672.0 ਃේጊἫญ✼ MRI-G01 34 46 54.0 139 21 18.2 19 䇸ർ䈱ጊ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪐㪆㪉䈎䉌㪞㪇㪈㫆䉕ᄌᦝ䋮 MRI-G01o* 34 46 42.9 139 21 16.0 25 䇸㘧ⴕ႐ධ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G02 34 46 28.5 139 24 9.0 224 䇸㪙㪫ὐ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪌㪆㪊䈎䉌㪞㪇㪉㫆䉕ᄌᦝ䋮 MRI-G02o* 34 46 9.9 139 24 15.5 270 䇸ጼ⾂᳓ᳰ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G03 34 45 58.7 139 22 26.9 188 䇸ᣥ᷹୥ᚲ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋨㪡㪤㪘㪀 MRI-G04 34 44 50.1 139 26 0.0 328 䇸ᅏጊ⍾Ṽ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G05 34 44 39.4 139 24 19.6 481 䇸ⵣ⍾Ṽർ᧲䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪏㪆㪎䈎䉌㪞㪇㪌㫆䉕ᄌᦝ䋮 MRI-G05o* 34 44 39.8 139 24 19.1 480 䇸ⵣ⍾Ṽർ᧲䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G07 34 44 16.7 139 22 49.7 558 䇸ᓮ␹Ἣ⨥ደ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋨㪡㪤㪘㪀 MRI-G09 34 44 21.7 139 25 12.7 439 䇸ⵣ⍾Ṽ᧲䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪏㪆㪎䈎䉌㪞㪇㪐㫆䉕ᄌᦝ䋮 MRI-G09o* 34 44 22.6 139 25 10.0 437 䇸ⵣ⍾Ṽ᧲䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G10 34 44 7.6 139 24 20.4 535 䇸ᰏᒻጊർ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G11 34 43 15.4 139 25 40.2 403 䇸Ꮕᧁ࿾ᬌ⍮✂䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G12 34 43 15.0 139 24 25.0 686 䇸⊕⍹ጊ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪏㪆㪎䈎䉌㪞㪈㪉㫆䉕ᄌᦝ䋮 MRI-G12o* 34 43 19.3 139 24 28.3 662 䇸⊕⍹ጊ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G13 34 42 27.2 139 22 52.5 180 䇸㑆ફᨋ㆏䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G14 34 42 45.3 139 24 46.4 615 䇸ੑሶጊ㪭㪦㪩㪫㪘㪚䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪎㪆㪎䈎䉌㪞㪈㪋㫆䉕ᄌᦝ䋮 MRI-G14o* 34 42 27.9 139 25 6.6 415 䇸ੑሶጊ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G15 34 42 7.9 139 22 11.9 32 䇸㊁Ⴧ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G16 34 42 8.3 139 26 35.2 37 䇸╩ፉ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G17 34 41 12.0 139 25 26.7 42 䇸Ꮕᧁ࿾䇹䋮㪞㪧㪪ㅪ⛯ὐ䋨㪡㪤㪘㪀 MRI-G18 34 44 46.5 139 23 30.8 555 䇸㎸┵䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G19 34 44 10.1 139 23 12.7 553 䇸㪘ὐ䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪌㪆㪈㪇䈎䉌㪞㪈㪐㫆䉕ᄌᦝ䋮 MRI-G19o* 34 44 11.9 139 23 10.8 548 䇸⴫⍾Ṽ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G20 34 43 41.0 139 23 24.8 675 䇸ਃේ␹␠䇹䋮㪞㪧㪪ㅪ⛯ὐ䋮㪉㪇㪇㪐㪆㪉䈎䉌㪜㪩㪠㪄㪤㪢䉕ᄌᦝ䋮 MRI-G21 34 43 31.2 139 23 27.9 703 䇸ਃේᣂጊ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G22 34 43 27.6 139 23 45.1 702 䇸ਃේἫሹධ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G23 34 43 41.7 139 23 57.4 733 䇸೶䉧ፄ䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G24 34 44 21.9 139 23 46.5 531 䇸㪙Ἣญ᧲䇹䋮㪞㪧㪪ㅪ⛯ὐ MRI-G25 34 44 18.5 139 22 52.1 557 䇸ᓮ␹Ἣዷᦸบ䇹䋮㪞㪧㪪➅䉍㄰䈚ὐ MRI-G26 34 47 21.9 139 23 28.8 3.3 䇸ጟ↰᷼䇹䋮㪞㪧㪪ㅪ⛯ὐ Site Note

Table 1 Description of gravity stations. Stations with an asterisk are currently unused. 気象研究所技術報告　第69号　2013

A. Takagi et al. Vol. 61

4

2004/3/30 Southern coast 11 10220 D109, CG3 A.Takagi, K.Fukui 2004/3/31 Inland 12 GOJINKACHAYA D109, CG3 A.Takagi, K.Fukui 2004/4/1 Northern coast 9 10220 D109, CG3 A.Takagi, K.Fukui

2004/7/27 Southern coast 16 GOJINKACHAYA D109, CG3 A.Takagi, K.Fujiwara, T.Yamamoto 2004/7/28 Circuit along the coast 10 D109, CG3 A.Takagi, K.Fujiwara, T.Yamamoto 2004/11/9 Inland 13 GOJINKACHAYA D109, CG3 A.Takagi, K.Fujiwara

2004/11/10 Southern coast 14 G04 D109, CG3 A.Takagi, K.Fujiwara 2004/11/11 Northern coast 7 G04 D109, CG3 A.Takagi, K.Fujiwara 2005/3/9 Northern coast 8 G09 D109, CG3 A.Takagi, K.Fujiwara 2005/3/10 Inland 9 GOJINKACHAYA D109, CG3 A.Takagi, K.Fujiwara 2005/3/11 Southern coast 4 G16 D109, CG3 A.Takagi, K.Fujiwara 2005/10/25 Inland 8 GOJINKACHAYA D109, CG3 A.Takagi, K.Fukui 2005/10/26 Southern coast 9 G11 D109, CG3 A.Takagi, K.Fukui 2005/10/27 Northern coast 10 G11 D109, CG3 A.Takagi, K.Fukui

2006/7/11 Northern coast 5 G04 D109, CG3 A.Takagi, H.Yamasato, H.Kuroki 2006/7/12 Southern coast 10 G04 D109, CG3 A.Takagi, H.Yamasato, H.Kuroki 2006/7/13 Climbing 11 GOJINKACHAYA D109, CG3 A.Takagi, H.Yamasato, H.Kuroki 2006/7/14 Caldera area 6 GOJINKACHAYA D109, CG3 A.Takagi, H.Yamasato

2007/3/16 Northern coast 7 960594 D109, CG3 A.Takagi, K.Fukui 2007/3/19 Southern coast 13 960594 D109, CG3 A.Takagi, T.Sakai 2007/3/22 Caldera area 7 GOJINKACHAYA D109, CG3 A.Takagi, T.Sakai 2007/7/23 Climbing 6 GOJINKACHAYA D109, CG3 A.Takagi, S.Ando 2007/7/24 Southern coast 12 G14 D109, CG3 A.Takagi, S.Ando 2007/7/25 Caldera area 8 GOJINKACHAYA D109, CG3 A.Takagi, S.Ando 2007/7/26 Northern coast 10 G14 D109, CG3 A.Takagi, S.Ando 2007/12/11 Southern coast 7 G14 D109, CG3 A.Takagi, K.Fukui 2007/12/16 Northern coast 11 G14 CG3 A.Takagi, K.Fukui 2007/12/19 Climbing 7 GOJINKACHAYA D109, CG3 A.Takagi, K.Fukui 2008/2/24 Southern coast 9 G14 D109, CG3 A.Takagi, H.Yamasato 2008/2/25 Northern coast 7 G14 D109, CG3 A.Takagi, H.Yamasato 2008/2/26 Climbing 8 GOJINKACHAYA CG3 A.Takagi, H.Yamasato 2008/7/25 Caldera area 7 GOJINKACHAYA D109, CG3, CG5 A.Takagi, H.Yamasato 2008/7/26 Southern coast 8 G14 D109, CG3, CG5 A.Takagi, H.Yamasato 2008/7/27 Northern coast 8 G14 D109, CG3, CG5 A.Takagi, H.Yamasato 2008/7/28 Climbing 8 GOJINKACHAYA D109, CG3, CG5 A.Takagi, H.Yamasato 2008/11/13 Southern coast 8 G14 D109, CG3, CG5 A.Takagi, K.Fukui 2008/11/14 Caldera area 8 G07 D109, CG3, CG5 A.Takagi, K.Fukui 2008/11/15 Northern coast 10 G14 D109, CG3, CG5 A.Takagi, K.Fukui 2008/11/16 Climbing 9 G07 D109, CG3, CG5 A.Takagi, K.Fukui 2009/2/20 Special round trips 3 G01 D109, CG3, CG5 A.Takagi, S.Ando 2009/2/21 Mt.Mihara 6 G07 D109, CG3, CG5 A.Takagi, S.Ando 2009/2/22 Caldera area 8 G07 CG3, CG5 A.Takagi, S.Ando 2009/2/23 Northern coast 6 G14 D109, CG5 A.Takagi, S.Ando

2009/2/24 Inland 8 G07 D109, CG3, CG5 A.Takagi, K.Fukui, S.Ando 2009/2/26 Climbing 6 G14 D109, CG3, CG5 A.Takagi, K.Fukui, S.Ando 2009/6/21 Mt.Mihara 7 G07 D109, CG3, CG5 A.Takagi, K.Fukui, T.Shimbori 2009/6/22 Southern coast 8 G14 D109, CG3 A.Takagi, K.Fukui, T.Shimbori 2009/6/23 Northern coast 8 G14 D109, CG5 A.Takagi, K.Fukui, T.Shimbori 2009/6/26 Caldera area 9 G07 D109, CG5 A.Takagi, K.Fukui, T.Shimbori Date Route Number of_stations Turning point Instrument Observer

Table 2 History of microgravity surveys. 気象研究所技術報告　第69号　2013

56

気象研究所技術報告　第69 号　2013

57

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᷹ὐᢙߪ_{4 ࡞࡯࠻ߣ߽ 10 ὐ⒟ᐲߢ޽ࠆޕฦ࡞࡯࠻ߦ߅} ߌࠆ᷹ቯᢙߦߪ⿠ὐߣ᛬㄰ߒὐ߽฽߻ޕᄤ୥╬ߩ⁁ᴫ ߦࠃࠅᓳ〝ߦ᷹ቯ߇ߢ߈ߥ߆ߞߚ᷹ὐߩᢙ߽฽߹ࠇߡ ޿ࠆ߇ޔ⸃ᨆಣℂߦߪᓔ〝ޔᓳ〝ߣ߽᷹ቯߒߚὐߩߺ ࠍ૶↪ߒߚޕ ߥ߅ޔᄢፉ᷹୥ᚲߩᑄᱛ߇_{2009 ᐕ 10 ᦬ߦ੍ቯߐࠇ} ߡ߅ࠅޔ࿕ቯὐߣߒߡ޿ߚ_{FGS ߇ᑄὐߣߥࠆน⢻ᕈ} ߇↢ߓߚߚ߼ޔઍᦧὐߩ୥⵬ߣߒߡ_{960595 ࠍㆬቯߒޔ} 2008 ᐕ 11 ᦬߆ࠄߪ⿠ὐ᷹ቯࠍ FGS ߣ 960595 ߩਔὐߢ ⴕߞߚޕ ฦ᷹ὐߢߪޔ㊀ജ᷹ቯ୯ߩ⵬ᱜߦ૶↪ߔࠆߚ߼ߩᯏ ᪾㜞㧔ၮḰὐ߆ࠄߩ㜞ߐ㧕ޔᄢ᳇࿶ࠍ᷹ቯߒߚޕ_{Fig. 2} ߦ᷹ቯ㘑᥊ߩ౮⌀ࠍ␜ߔޕ

3㧚᷹ቯ⚿ᨐ

ᦨ⚳⊛ߥ⋧ኻ㊀ജ୯ࠍ▚಴ߔࠆߚ߼ߦ૶↪ߔࠆ࠺࡯ ࠲ߩ᧦ઙߪޔ_{2 บએ਄ߩ㊀ജ⸘ߦࠃࠆޔᓔᓳ᷹ቯ୯߇} ޽ࠆ߽ߩߣߒޔߘࠇએᄖߪ㒰ᄖߒߚޕᰴߦ᷹ቯ୯ߦᯏ ᪾㜞⵬ᱜޔ᳇࿶⵬ᱜޔầ᳤⵬ᱜޔ࠼࡝ࡈ࠻⵬ᱜޔ෸߮ 㒠᳓⵬ᱜࠍⴕߞߚޕᯏ᪾㜞⵬ᱜߪߘࠇߙࠇߩ㊀ജ⸘ߦ ኻߒߡ᷹ቯߒߚᯏ᪾㜞ߦࡈ࡝࡯ࠛࠕ࡯൨㈩㧔㧙_0.3086 mgal/m㧕ࠍਸ਼ߓߚ୯ࠍᏅߒᒁ޿ߚޕ᳇࿶⵬ᱜߪޔ᷹ὐ ߢ⸘᷹ߒߚ⃻࿾᳇࿶ߣᮡḰ᳇࿶_{1013.25㧔hPa㧕ߣߩ⋧} ኻᏅߦ⵬ᱜଥᢙ㧙_{0.0003㧔mgal/hPa㧕ࠍਸ਼ߓߚ୯ࠍᏅ} ߒᒁ޿ߚޕầ᳤⵬ᱜߪ࿕૕ầ᳤ߣᶏᵗầ᳤ࠍ⸘▚ߔࠆ ࡊ ࡠ ࠣ ࡜ ࡓ_{GOTIC2㧔Matsumoto et al., 2001㧕 ࠍ ↪ ޿} ߚޕ_{1066A ࿾⃿ࡕ࠺࡞㧔ᄢਭ଻࡮㆙⮮, 1983㧕ߦၮߠߊ} Green 㑐ᢙࠍㆬᛯߒޔTamura 㧔1982㧕ߩࡐ࠹ࡦࠪࡖ࡞ࠍ ⠨ᘦߒޔ_{50 m ࡔ࠶ࠪࡘߢ⸘▚ߒߚޕ㒠᳓ߩ㊀ജߦ෸߷} ߔᓇ㗀ߪޔᷰㄝ࡮ઁ㧔_{1990㧕߇᜛ᢔࡕ࠺࡞ߦࠃࠆᚻᴺ} ࠍឭ᩺ߒߡ޿ࠆޕᷰㄝ࡮ઁ㧔_{1990㧕ߪޔ1987㨪1989 ᐕ} ߩ_{13 ࿁ߩ㊀ജ᷹ቯ୯ࠍ↪޿ޔદ⼺ᄢፉࠍ⋥ᓘ 10 km ߩ} ౞⋚ߦㄭૃߒޔߘߩ๟ㄝߢ᳓૏࠯ࡠߣ޿߁Ⴚ⇇᧦ઙߩ ਅߢᦨㆡߩ᜛ᢔଥᢙࠍ᳞߼ߚޕዊ⺰ߦ߅޿ߡ߽ޔߘࠇ ߣหߓ᜛ᢔଥᢙ_{0.2 m}2_{/sec ࠍ↪޿ޔห᭽ߦ㒠᳓ߩ㊀ജߦ} ෸߷ߔᓇ㗀ࠍ⵬ᱜߒߚޕߥ߅ޔᣣ㒠᳓㊂ߪᄢፉ᷹୥ᚲ 㧔_{FGS㧕ߩ࠺࡯࠲ࠍ↪޿ߚޕ} એ਄ߩ⵬ᱜಣℂᓟޔࡃࡀᝄࠅሶߦ⿠࿃ߔࠆ࠼࡝ࡈ࠻ ⵬ᱜࠍⴕߞߚޕᓔ〝ߣᓳ〝ߩ㊀ജ᷹ቯ୯ߩᏅࠍ᷹ቯ㑆㓒ߩᤨ㑆ߦኻߒߡࡊࡠ࠶࠻ߒޔߘߩ࠼࡝ࡈ࠻൨㈩ࠍᦨ ዊ⥄ਸ਼ᴺߢ᳞߼ߚޕᓔᓳߩ᷹ቯᤨ㑆ਛߪߎߩ࠼࡝ࡈ࠻ ଥᢙߢ㊀ജ୯߇⋥✢⊛ߦᄌൻߒߡ޿ࠆߣ઒ቯߒߡ࠼࡝ ࡈ࠻⵬ᱜࠍⴕ߁ޕߒ߆ߒޔㆇ៝ᤨ޽ࠆ޿ߪࠤ࡯ࠬߩ಴ ߒ౉ࠇߩ㓙ߩ㊀ജ⸘ߦਈ߃ࠄࠇߚ࡚ࠪ࠶ࠢߦࠃࠆ࠹ࠕ 㧔࠺࡯࠲ߩߣ߮㧕߇޽ࠆߣޔߎߩ࠼࡝ࡈ࠻൨㈩ߪ⋥✢ߦ ߩࠄߥ޿ޕ⋥✢߆ࠄᄢ߈ߊߪߕࠇߚ႐วߦߪ࠼࡝ࡈ࠻ ⵬ᱜߔࠆߎߣ߇࿎㔍ߢ޽ࠆޕㄭૃ⋥✢ߩ_{R-2 ਸ਼୯߇᭎} ߨ_{0.75 ࠃࠅዊߐ޿႐วߩ࠺࡯࠲ߪណ↪ߒߥ޿ߎߣߣߒ} ߚޕ ߎࠇࠄߩಣℂࠍᣉߒߚᓟޔ_{2 บએ਄ߩ࠺࡯࠲߇޽ࠆ႐} วߩ_{FGS ࠍ࿕ቯὐߣߔࠆ⋧ኻ㊀ജ୯ߩන⚐ᐔဋࠍฦὐ} ߩᦨ⚳㊀ജ୯ߣߒߚޕ_{Fig. 3 ߦᦨ⚳㊀ജ୯߇ 2 ࿁એ਄ሽ} ࿷ߔࠆ_{42 ࿾ὐߩᦨ⚳㊀ജ୯ߩᤨ♽೉࿑ࠍ␜ߔޕ᷹ቯ♖} ᐲߩ⋡቟ࠍޔᓔ〝ߣᓳ〝ߩ᷹ቯ୯ߩᐔဋ୯߆ࠄߩセᏅ ߣޔⶄᢙบߩ㊀ജ⸘ߦࠃࠆ᷹ቯ୯ߩᮡḰ஍Ꮕߩ๺ߣߒޔ Fig. 3 ߩࠛ࡜࡯ࡃ࡯ߦ␜ߒߚޕ ߥ߅ޔ⥄േ㊀ജ⸘ߢߪ᷹ቯᤨ㑆ਛߩ㊀ജ୯ߩᮡḰ஍ Ꮕ߽⥄േ⊛ߦ▚಴ߐࠇࠆޕ_{60 ⑽ 3 ࿁ߩ᷹ቯߢᓧࠄࠇ} ߚᮡḰ஍Ꮕߩᐔဋߪ_{0.02㨪0.2 mgal ߩ▸࿐ߦ෼߹ࠆߎ} ߣ߇ᄙ޿߇ޔᤨߦ_{0.4 mgal ߦ߽㆐ߔࠆߣ߈߇޽ߞߚޕ} ߎࠇߪᄢፉ߇ᶏᵗ਄ߦ޽ࠆߚ߼ᒝ޿ᵄᶉߩ޽ࠆᤨߦ᷹ ቯߒߚ႐วߦߪޔ㊀ജ୯ߦᄢ߈ߥࡁࠗ࠭ߣߒߡ㊀⇥ߔ ࠆ߆ࠄߢ޽ࠆޕౝ㒽ߩ᷹ⷰὐߪᲧセ⊛ᵄᶉࡁࠗ࠭ߪዋ ߥ޿߇㧔଀߃߫ޔ_{G18ޔG24ޔG25 ╬㧕ޔᶏጯᴪ޿ޔߣ} ࠅࠊߌᄖᵗߦ㕙ߒߚධ⷏ᶏጯᴪ޿ߩᵄᶉࡁࠗ࠭ߪޔቯ Ᏹ⊛ߦᄢ߈߆ߞߚ㧔଀߃߫ޔ_{93055ޔG15ޔG17 ╬㧕ޕ} Fig. 3 ࠍ⷗ࠆߣޔ᷹ὐߦࠃߞߡߪ᣿ࠄ߆ߥ㊀ജ୯ߩ⚻ ᐕᄌൻࠍ␜ߔ᷹ⷰὐ߇޽ࠆߎߣߦ᳇ߠߊޕࠃࠅㆡಾߥ ⹏ଔࠍⴕ߁ߚ߼ߦޔᦨ⚳୯߇_{3 ᐕએ਄ߦࠊߚߞߡߩߴ} 5 ࿁એ਄ሽ࿷ߔࠆ 22 ᷹ὐࠍㆬ߮ޔ߁ߜ 18 ᷹ὐࠍ␜ߒ ߚ߽ߩ߇_{Fig. 4 ߢ޽ࠆޕዪ࿾⊛ߦ㗼⪺ߥ࿾Ზᄌേ߇⍮} ࠄࠇߡ޿ࠆਃේᣂጊ๟ㄝߩ᷹ὐ_{4 ὐ㧔G05ޔG22ޔG24ޔ} G25㧕ߪ㒰ᄖߒߚޕᦨ⚳㊀ജ୯ࠍᤨ㑆ߦኻߒߡ✢ᒻㄭ ૃߒߚ⋥✢ߣޔߘߩᄌൻㅦᐲ෸߮ផቯ㊂ߩ_{1 σ ߩᮡḰ} ஍Ꮕ߽␜ߒߚޕ࠺࡯࠲ߩ߫ࠄߟ߈߽ᄢ߈ߊ࠺࡯࠲ᢙ߽ චಽߣߪ޿߃ߥ޿᷹ὐ߽޽ࠆ߇ޔ_{5 ᐕߣ޿߁⍴ᦼ㑆ߦ} ߅޿ߡ⚻ᐕᄌൻ߇⷗ߡขࠇࠆ᷹ὐ߽޽ࠆޕߘߩ․ᓽߪޔ ౝ㒽ߩࠞ࡞࠺࡜ർㇱ๟ㄝߩ᷹ὐ߶ߤ㊀ജ୯ߪᷫዋߒ 㧔_{ONSENHOTELޔO1003ޔO1004 ╬㧕ޔߘߎ߆ࠄ㔌ࠇࠆ} ᷹ὐ߶ߤჇᄢߔࠆ㧔_{G01oޔ93055 ╬㧕ޕ㊀ജ୯ߪ࿾Ზᄌ} േߦࠃࠅ㓉⿠ߔࠆߎߣߢᷫዋߔࠆޕࠃߞߡߎߩ⚿ᨐߪޔ ৻ᰴㄭૃ⊛ߦߪࠞ࡞࠺࡜ർㇱ๟ㄝ߇⋧ኻ⊛ߦ㓉⿠ߒߡ ޿ࠆߎߣࠍ␜ߒߡ޿ࠆߩ߆߽ߒࠇߥ޿ޕߎࠇࠄߩ⚿ᨐ ࠍ_{Table 3 ߦ␜ߔޕ}

4㧚࿶ജḮផቯ

࿾Ზᄌേ᷹ⷰߦࠃߞߡદ⼺ᄢፉߢߪ⚻ᐕ⊛ߥ⤘ᒛ߇ ᷹ⷰߐࠇߡ޿ࠆ㧔㜞ᧁ࡮ઁ, 2008㧕ޕᄌേࡄ࠲࡯ࡦߪᤨ

Fig. 2 Measuring microgravity with gravity meters at G22 on Mt. Miharayama, on January 14, 2006.

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Relative Precise Gravity Survey at Izu-Oshima Volcano in the Eruption Preparation Period 2010 5 ᷹ὐᢙߪ_{4 ࡞࡯࠻ߣ߽ 10 ὐ⒟ᐲߢ޽ࠆޕฦ࡞࡯࠻ߦ߅} ߌࠆ᷹ቯᢙߦߪ⿠ὐߣ᛬㄰ߒὐ߽฽߻ޕᄤ୥╬ߩ⁁ᴫ ߦࠃࠅᓳ〝ߦ᷹ቯ߇ߢ߈ߥ߆ߞߚ᷹ὐߩᢙ߽฽߹ࠇߡ ޿ࠆ߇ޔ⸃ᨆಣℂߦߪᓔ〝ޔᓳ〝ߣ߽᷹ቯߒߚὐߩߺ ࠍ૶↪ߒߚޕ ߥ߅ޔᄢፉ᷹୥ᚲߩᑄᱛ߇_{2009 ᐕ 10 ᦬ߦ੍ቯߐࠇ} ߡ߅ࠅޔ࿕ቯὐߣߒߡ޿ߚ_{FGS ߇ᑄὐߣߥࠆน⢻ᕈ} ߇↢ߓߚߚ߼ޔઍᦧὐߩ୥⵬ߣߒߡ_{960595 ࠍㆬቯߒޔ} 2008 ᐕ 11 ᦬߆ࠄߪ⿠ὐ᷹ቯࠍ FGS ߣ 960595 ߩਔὐߢ ⴕߞߚޕ ฦ᷹ὐߢߪޔ㊀ജ᷹ቯ୯ߩ⵬ᱜߦ૶↪ߔࠆߚ߼ߩᯏ ᪾㜞㧔ၮḰὐ߆ࠄߩ㜞ߐ㧕ޔᄢ᳇࿶ࠍ᷹ቯߒߚޕ_{Fig. 2} ߦ᷹ቯ㘑᥊ߩ౮⌀ࠍ␜ߔޕ

3㧚᷹ቯ⚿ᨐ

ᦨ⚳⊛ߥ⋧ኻ㊀ജ୯ࠍ▚಴ߔࠆߚ߼ߦ૶↪ߔࠆ࠺࡯ ࠲ߩ᧦ઙߪޔ_{2 บએ਄ߩ㊀ജ⸘ߦࠃࠆޔᓔᓳ᷹ቯ୯߇} ޽ࠆ߽ߩߣߒޔߘࠇએᄖߪ㒰ᄖߒߚޕᰴߦ᷹ቯ୯ߦᯏ ᪾㜞⵬ᱜޔ᳇࿶⵬ᱜޔầ᳤⵬ᱜޔ࠼࡝ࡈ࠻⵬ᱜޔ෸߮ 㒠᳓⵬ᱜࠍⴕߞߚޕᯏ᪾㜞⵬ᱜߪߘࠇߙࠇߩ㊀ജ⸘ߦ ኻߒߡ᷹ቯߒߚᯏ᪾㜞ߦࡈ࡝࡯ࠛࠕ࡯൨㈩㧔㧙_0.3086 mgal/m㧕ࠍਸ਼ߓߚ୯ࠍᏅߒᒁ޿ߚޕ᳇࿶⵬ᱜߪޔ᷹ὐ ߢ⸘᷹ߒߚ⃻࿾᳇࿶ߣᮡḰ᳇࿶_{1013.25㧔hPa㧕ߣߩ⋧} ኻᏅߦ⵬ᱜଥᢙ㧙_{0.0003㧔mgal/hPa㧕ࠍਸ਼ߓߚ୯ࠍᏅ} ߒᒁ޿ߚޕầ᳤⵬ᱜߪ࿕૕ầ᳤ߣᶏᵗầ᳤ࠍ⸘▚ߔࠆ ࡊ ࡠ ࠣ ࡜ ࡓ_{GOTIC2㧔Matsumoto et al., 2001㧕 ࠍ ↪ ޿} ߚޕ_{1066A ࿾⃿ࡕ࠺࡞㧔ᄢਭ଻࡮㆙⮮, 1983㧕ߦၮߠߊ} Green 㑐ᢙࠍㆬᛯߒޔTamura 㧔1982㧕ߩࡐ࠹ࡦࠪࡖ࡞ࠍ ⠨ᘦߒޔ_{50 m ࡔ࠶ࠪࡘߢ⸘▚ߒߚޕ㒠᳓ߩ㊀ജߦ෸߷} ߔᓇ㗀ߪޔᷰㄝ࡮ઁ㧔_{1990㧕߇᜛ᢔࡕ࠺࡞ߦࠃࠆᚻᴺ} ࠍឭ᩺ߒߡ޿ࠆޕᷰㄝ࡮ઁ㧔_{1990㧕ߪޔ1987㨪1989 ᐕ} ߩ_{13 ࿁ߩ㊀ജ᷹ቯ୯ࠍ↪޿ޔદ⼺ᄢፉࠍ⋥ᓘ 10 km ߩ} ౞⋚ߦㄭૃߒޔߘߩ๟ㄝߢ᳓૏࠯ࡠߣ޿߁Ⴚ⇇᧦ઙߩ ਅߢᦨㆡߩ᜛ᢔଥᢙࠍ᳞߼ߚޕዊ⺰ߦ߅޿ߡ߽ޔߘࠇ ߣหߓ᜛ᢔଥᢙ_{0.2 m}2_{/sec ࠍ↪޿ޔห᭽ߦ㒠᳓ߩ㊀ജߦ} ෸߷ߔᓇ㗀ࠍ⵬ᱜߒߚޕߥ߅ޔᣣ㒠᳓㊂ߪᄢፉ᷹୥ᚲ 㧔_{FGS㧕ߩ࠺࡯࠲ࠍ↪޿ߚޕ} એ਄ߩ⵬ᱜಣℂᓟޔࡃࡀᝄࠅሶߦ⿠࿃ߔࠆ࠼࡝ࡈ࠻ ⵬ᱜࠍⴕߞߚޕᓔ〝ߣᓳ〝ߩ㊀ജ᷹ቯ୯ߩᏅࠍ᷹ቯ㑆㓒ߩᤨ㑆ߦኻߒߡࡊࡠ࠶࠻ߒޔߘߩ࠼࡝ࡈ࠻൨㈩ࠍᦨ ዊ⥄ਸ਼ᴺߢ᳞߼ߚޕᓔᓳߩ᷹ቯᤨ㑆ਛߪߎߩ࠼࡝ࡈ࠻ ଥᢙߢ㊀ജ୯߇⋥✢⊛ߦᄌൻߒߡ޿ࠆߣ઒ቯߒߡ࠼࡝ ࡈ࠻⵬ᱜࠍⴕ߁ޕߒ߆ߒޔㆇ៝ᤨ޽ࠆ޿ߪࠤ࡯ࠬߩ಴ ߒ౉ࠇߩ㓙ߩ㊀ജ⸘ߦਈ߃ࠄࠇߚ࡚ࠪ࠶ࠢߦࠃࠆ࠹ࠕ 㧔࠺࡯࠲ߩߣ߮㧕߇޽ࠆߣޔߎߩ࠼࡝ࡈ࠻൨㈩ߪ⋥✢ߦ ߩࠄߥ޿ޕ⋥✢߆ࠄᄢ߈ߊߪߕࠇߚ႐วߦߪ࠼࡝ࡈ࠻ ⵬ᱜߔࠆߎߣ߇࿎㔍ߢ޽ࠆޕㄭૃ⋥✢ߩ_{R-2 ਸ਼୯߇᭎} ߨ_{0.75 ࠃࠅዊߐ޿႐วߩ࠺࡯࠲ߪណ↪ߒߥ޿ߎߣߣߒ} ߚޕ ߎࠇࠄߩಣℂࠍᣉߒߚᓟޔ_{2 บએ਄ߩ࠺࡯࠲߇޽ࠆ႐} วߩ_{FGS ࠍ࿕ቯὐߣߔࠆ⋧ኻ㊀ജ୯ߩන⚐ᐔဋࠍฦὐ} ߩᦨ⚳㊀ജ୯ߣߒߚޕ_{Fig. 3 ߦᦨ⚳㊀ജ୯߇ 2 ࿁એ਄ሽ} ࿷ߔࠆ_{42 ࿾ὐߩᦨ⚳㊀ജ୯ߩᤨ♽೉࿑ࠍ␜ߔޕ᷹ቯ♖} ᐲߩ⋡቟ࠍޔᓔ〝ߣᓳ〝ߩ᷹ቯ୯ߩᐔဋ୯߆ࠄߩセᏅ ߣޔⶄᢙบߩ㊀ജ⸘ߦࠃࠆ᷹ቯ୯ߩᮡḰ஍Ꮕߩ๺ߣߒޔ Fig. 3 ߩࠛ࡜࡯ࡃ࡯ߦ␜ߒߚޕ ߥ߅ޔ⥄േ㊀ജ⸘ߢߪ᷹ቯᤨ㑆ਛߩ㊀ജ୯ߩᮡḰ஍ Ꮕ߽⥄േ⊛ߦ▚಴ߐࠇࠆޕ_{60 ⑽ 3 ࿁ߩ᷹ቯߢᓧࠄࠇ} ߚᮡḰ஍Ꮕߩᐔဋߪ_{0.02㨪0.2 mgal ߩ▸࿐ߦ෼߹ࠆߎ} ߣ߇ᄙ޿߇ޔᤨߦ_{0.4 mgal ߦ߽㆐ߔࠆߣ߈߇޽ߞߚޕ} ߎࠇߪᄢፉ߇ᶏᵗ਄ߦ޽ࠆߚ߼ᒝ޿ᵄᶉߩ޽ࠆᤨߦ᷹ ቯߒߚ႐วߦߪޔ㊀ജ୯ߦᄢ߈ߥࡁࠗ࠭ߣߒߡ㊀⇥ߔ ࠆ߆ࠄߢ޽ࠆޕౝ㒽ߩ᷹ⷰὐߪᲧセ⊛ᵄᶉࡁࠗ࠭ߪዋ ߥ޿߇㧔଀߃߫ޔ_{G18ޔG24ޔG25 ╬㧕ޔᶏጯᴪ޿ޔߣ} ࠅࠊߌᄖᵗߦ㕙ߒߚධ⷏ᶏጯᴪ޿ߩᵄᶉࡁࠗ࠭ߪޔቯ Ᏹ⊛ߦᄢ߈߆ߞߚ㧔଀߃߫ޔ_{93055ޔG15ޔG17 ╬㧕ޕ} Fig. 3 ࠍ⷗ࠆߣޔ᷹ὐߦࠃߞߡߪ᣿ࠄ߆ߥ㊀ജ୯ߩ⚻ ᐕᄌൻࠍ␜ߔ᷹ⷰὐ߇޽ࠆߎߣߦ᳇ߠߊޕࠃࠅㆡಾߥ ⹏ଔࠍⴕ߁ߚ߼ߦޔᦨ⚳୯߇_{3 ᐕએ਄ߦࠊߚߞߡߩߴ} 5 ࿁એ਄ሽ࿷ߔࠆ 22 ᷹ὐࠍㆬ߮ޔ߁ߜ 18 ᷹ὐࠍ␜ߒ ߚ߽ߩ߇_{Fig. 4 ߢ޽ࠆޕዪ࿾⊛ߦ㗼⪺ߥ࿾Ზᄌേ߇⍮} ࠄࠇߡ޿ࠆਃේᣂጊ๟ㄝߩ᷹ὐ_{4 ὐ㧔G05ޔG22ޔG24ޔ} G25㧕ߪ㒰ᄖߒߚޕᦨ⚳㊀ജ୯ࠍᤨ㑆ߦኻߒߡ✢ᒻㄭ ૃߒߚ⋥✢ߣޔߘߩᄌൻㅦᐲ෸߮ផቯ㊂ߩ_{1 σ ߩᮡḰ} ஍Ꮕ߽␜ߒߚޕ࠺࡯࠲ߩ߫ࠄߟ߈߽ᄢ߈ߊ࠺࡯࠲ᢙ߽ චಽߣߪ޿߃ߥ޿᷹ὐ߽޽ࠆ߇ޔ_{5 ᐕߣ޿߁⍴ᦼ㑆ߦ} ߅޿ߡ⚻ᐕᄌൻ߇⷗ߡขࠇࠆ᷹ὐ߽޽ࠆޕߘߩ․ᓽߪޔ ౝ㒽ߩࠞ࡞࠺࡜ർㇱ๟ㄝߩ᷹ὐ߶ߤ㊀ജ୯ߪᷫዋߒ 㧔_{ONSENHOTELޔO1003ޔO1004 ╬㧕ޔߘߎ߆ࠄ㔌ࠇࠆ} ᷹ὐ߶ߤჇᄢߔࠆ㧔_{G01oޔ93055 ╬㧕ޕ㊀ജ୯ߪ࿾Ზᄌ} േߦࠃࠅ㓉⿠ߔࠆߎߣߢᷫዋߔࠆޕࠃߞߡߎߩ⚿ᨐߪޔ ৻ᰴㄭૃ⊛ߦߪࠞ࡞࠺࡜ർㇱ๟ㄝ߇⋧ኻ⊛ߦ㓉⿠ߒߡ ޿ࠆߎߣࠍ␜ߒߡ޿ࠆߩ߆߽ߒࠇߥ޿ޕߎࠇࠄߩ⚿ᨐ ࠍ_{Table 3 ߦ␜ߔޕ}

4㧚࿶ജḮផቯ

࿾Ზᄌേ᷹ⷰߦࠃߞߡદ⼺ᄢፉߢߪ⚻ᐕ⊛ߥ⤘ᒛ߇ ᷹ⷰߐࠇߡ޿ࠆ㧔㜞ᧁ࡮ઁ, 2008㧕ޕᄌേࡄ࠲࡯ࡦߪᤨ

Fig. 2 Measuring microgravity with gravity meters at G22 on Mt. Miharayama, on January 14, 2006.

6

Fig. 3 Gravity changes of all stations referenced to FGS. 気象研究所技術報告　第69号　2013

58

59

(8)

㑆ⓨ㑆⊛ߦⶄ㔀ߢ޽ࠅޔߎࠇࠍන⚐ߥࡕ࠺࡞ߢ⺑᣿ߔ ࠆߎߣߪ࿎㔍ߢ޽ࠆ߇ޔ╬ᣇ⊛ߥ⤘ᒛᕈߩᄌേ߆ࠄ৻ ᰴㄭૃ⊛ߦߪ⃿⁁࿶ജḮࠍ઒ቯߔࠆߎߣߢ໧㗴ߪߥ޿ޕ ߘߎߢޔએਅޔદ⼺ᄢፉߩᄌേࠍන৻ߩ⃿⁁࿶ജḮߢ ↢ߓߚ߽ߩߣ઒ቯߒߡ⸃ᨆߔࠆޕ ৻⥸ߦ࿾ਅߢ๟ㄝኒᐲߣ⇣ߥࠆ‛⾰߇లႯߐࠇߚ ᤨޔ࿾⴫㕙ߢߪ࿾Ზᄌേ߇᷹ⷰߐࠇࠆߣߣ߽ߦޔ㊀ജ ᄌൻ߽᷹ⷰߐࠇࠆޕ⪤ේ㧔_{1977㧕ߪ⨃ᧁࡕ࠺࡞㧔Mogi,} 1958㧕ࠍၮߦޔ⃿⁁࿶ജḮߦࠃࠅᒢᕈ૕ߩ࿾⴫ߢ↢ߓ ࠆ㊀ജᄌൻߩℂ⺰ᑼࠍ␜ߒߚޕ ㊀ജᄌൻ_{E g ߪޔએਅߩ}_{4 ߟߩᚑಽߩ✚๺߆ࠄߥࠆޕ} 1 㧚᷹ὐ߇㓉⿠ߔࠆߎߣߦࠃߞߡᄌൻߔࠆࡈ࡝࡯ࠛࠕ࡯ ߩᚑಽ_E_f 2 㧚ኒᐲߩ⇣ߥࠆ⃿ߩ૕Ⓧᄌൻߦࠃࠆᚑಽ Eg0 3 㧚㓉⿠ߒߚ⾰㊂ߦࠃࠆᚑಽ Eg1 4 㧚⃿Ზ߇⤘ᒛߔࠆߎߣߦࠃࠅ๟ㄝߩᒢᕈ૕ߦ↢ߓࠆ ኒᐲᄌൻߦࠃࠆᚑಽ_{E g}₂ ޿߹ਁ᦭ᒁജቯᢙࠍG㧔= 6.67 10-11_m3_kg-1_s-2㧕ޔࡈ Fig. 4 Averaged gravity change rates with Std. Error (1σ) at the major stations except stations on and around Mt. Miharayama,

(9)

Relative Precise Gravity Survey at Izu-Oshima Volcano in the Eruption Preparation Period 2010 7 㑆ⓨ㑆⊛ߦⶄ㔀ߢ޽ࠅޔߎࠇࠍන⚐ߥࡕ࠺࡞ߢ⺑᣿ߔ ࠆߎߣߪ࿎㔍ߢ޽ࠆ߇ޔ╬ᣇ⊛ߥ⤘ᒛᕈߩᄌേ߆ࠄ৻ ᰴㄭૃ⊛ߦߪ⃿⁁࿶ജḮࠍ઒ቯߔࠆߎߣߢ໧㗴ߪߥ޿ޕ ߘߎߢޔએਅޔદ⼺ᄢፉߩᄌേࠍන৻ߩ⃿⁁࿶ജḮߢ ↢ߓߚ߽ߩߣ઒ቯߒߡ⸃ᨆߔࠆޕ ৻⥸ߦ࿾ਅߢ๟ㄝኒᐲߣ⇣ߥࠆ‛⾰߇లႯߐࠇߚ ᤨޔ࿾⴫㕙ߢߪ࿾Ზᄌേ߇᷹ⷰߐࠇࠆߣߣ߽ߦޔ㊀ജ ᄌൻ߽᷹ⷰߐࠇࠆޕ⪤ේ㧔_{1977㧕ߪ⨃ᧁࡕ࠺࡞㧔Mogi,} 1958㧕ࠍၮߦޔ⃿⁁࿶ജḮߦࠃࠅᒢᕈ૕ߩ࿾⴫ߢ↢ߓ ࠆ㊀ജᄌൻߩℂ⺰ᑼࠍ␜ߒߚޕ ㊀ജᄌൻ_{E g ߪޔએਅߩ}_{4 ߟߩᚑಽߩ✚๺߆ࠄߥࠆޕ} 1 㧚᷹ὐ߇㓉⿠ߔࠆߎߣߦࠃߞߡᄌൻߔࠆࡈ࡝࡯ࠛࠕ࡯ ߩᚑಽ_E_f 2 㧚ኒᐲߩ⇣ߥࠆ⃿ߩ૕Ⓧᄌൻߦࠃࠆᚑಽ Eg0 3 㧚㓉⿠ߒߚ⾰㊂ߦࠃࠆᚑಽ Eg1 4 㧚⃿Ზ߇⤘ᒛߔࠆߎߣߦࠃࠅ๟ㄝߩᒢᕈ૕ߦ↢ߓࠆ ኒᐲᄌൻߦࠃࠆᚑಽ_{E g}₂ ޿߹ਁ᦭ᒁജቯᢙࠍG㧔= 6.67 10-11_m3_kg-1_s-2㧕ޔࡈ Fig. 4 Averaged gravity change rates with Std. Error (1σ) at the major stations except stations on and around Mt. Miharayama,

ref-erenced to FGS.

8 ࡝࡯ࠛࠕ࡯൨㈩ࠍCf㧔mgal/m㧕ޔ⃿ᲖౝㇱߦలႯߐࠇߚ ‛⾰ߩኒᐲࠍ_S₀ޔ๟ㄝᒢᕈ૕ߩኒᐲࠍ_{Sޔ࡜ࡔቯᢙࠍ Mޔ} N ߣߔࠆޕ࿾⴫㕙߆ࠄᷓߐ D ߦ޽ࠆ⃿Ზ߇╬࿶⤘ᒛߒޔ ⃿⁁࿶ജḮߩ૕Ⓧᄌൻ㊂߇_{EV ߣߥߞߚߣ߈ޔ࿾⴫㕙ߩ} ࿶ജḮ⋥਄߆ࠄߩ᳓ᐔ〒㔌_{r ߦ߅ߌࠆ㊀ജᄌൻߩᚑಽ} ߪޔ⪤ේ㧔_{1977㧕߆ࠄߘࠇߙࠇએਅߩㅢࠅߦ⴫ߖࠆޕ} E E Q f V C D r D f 3 4 ₍ 2 2 3 2₎/ 㧔1㧕 Eg G VE S S D r D 0 ( 0 )₍ 2 2 3 2₎/ 㧔2㧕 E E S M N M N g G V D r D 1 2 2 3 2 2 ( ) ( )/ 㧔3㧕 E E SN M N g G V D r D 2 ₍ 2 2 3 2₎/ 㧔4㧕 ߎࠇࠄߩ✚๺_{E g ߪએਅߩࠃ߁ߥ◲නߥᒻߦ⴫ߖࠆޕ} E E E E E E Q E S g f g g g C V G V D r D f «¬®® ®® º » ®® ¼®® 0 1 2 0 2 2 3 2 3 4 ( )/ 㧔5㧕 ߎߩ߁ߜਛ᜝ᒐౝߩ╙_{1 㗄ߪ Ef ߦ⋧ᒰߒޔ⨃ᧁ࠰࡯} ࠬߦၮߠߊ㓉⿠ߦࠃࠆࡈ࡝࡯ࠛࠕ࡯ߩነਈಽߢ޽ࠅޔ ╙_{2 㗄ߪߘࠇએᄖߩነਈಽߩ✚๺ߢ޽ࠆޕਛ᜝ᒐߩᄖ} ߩ㗄ߪ࿶ജḮߣ᷹ὐߩ૏⟎㑐ଥߦࠃࠆᷫ⴮㗄ࠍᗧ๧ߔ ࠆޕߎࠇࠍ⷗ߡࠊ߆ࠆࠃ߁ߦޔ_{E g ߪ྾ߟߩ㗄߇࿾Ზᄌ} േߦ઻߁ࡈ࡝࡯ࠛࠕ࡯ነਈಽߣ⃿Ზౝߩ‛⾰߇૕Ⓧ⤘ ᒛߒߚ⾰㊂ߦ઻߁㊀ജᄌൻߩነਈಽߩ๺ߛߌߩ◲නߥ ᑼߢ⴫ߐࠇࠆߎߣ߇ࠊ߆ࠆޕ દ⼺ᄢፉߩᄌേߦ⨃ᧁࡕ࠺࡞ࠍㆡ↪ߒޔᚒޘ߇ᓧߚ 18 ᷹ὐߩ㊀ജᄌൻㅦᐲࠍᑼ㧔5㧕ߦ޽ߡߪ߼ޔᩰሶὐត ⚝ᴺߦࠃࠅᱷᏅ⥄ਸ਼๺߇ᦨዊߦߥࠆࠃ߁ߥ࿶ജḮߩ✲ ᐲޔ⚻ᐲޔᷓߐ_{Dޔ૕Ⓧᄌൻ㊂ EV ߩᦨㆡ⸃ࠍផቯߒߚޕ} ࡈ࡝࡯ࠛࠕ࡯൨㈩_C_fߪ㧙_{0.3086 mgal/mޔ⃿Ზౝߩኒᐲ} S0ࠍ 2.67 103 kg/m3ߣߒߚޕ૏⟎ߩត⚝ᩰሶ㑆㓒ߪ0.05 kmޔ૕Ⓧᄌൻ㊂ߩត⚝ᩰሶ㑆㓒ߪ 0.1 106_m3_{/year ߣ} ߒޔ᷹ὐߩᮡ㜞Ꮕߦࠃࠆ⵬ᱜ߽ⴕߞߚ㧔⑔੗࡮ઁ_{, 2003㧕ޕ} ᳞߹ߞߚ࿶ജḮࡄ࡜ࡔ࡯࠲ߪޔࠞ࡞࠺࡜✼ർㇱ㧔_34.7523 °Nޔ139.4078°EޔONSENHOTEL ߩධ 150 mޔ᧲ 450 m㧕 ߩᶏᛮਅ_{3.65 km ߢޔ૕Ⓧᄌൻㅦᐲߪ 7.6 10}6_m3_/year ߢ޽ߞߚޕ㊀ജᄌൻㅦᐲߩᱷᏅߩᮡḰ஍Ꮕߪޔ_0.0042 mgal/year ߢ޽ߞߚޕFig. 5 ߦޔ࿶ജḮߩᦨㆡ୯ߣߒߡ ផቯߐࠇߚ႐ᚲࠍᤊශߢ␜ߔޕ߹ߚޔฦ᷹ⷰὐߩ㊀ജ ᄌൻㅦᐲߦ_{1 T ߩᮡḰ஍Ꮕࠍ⠨ᘦߒߡ⸘▚ߐࠇࠆޔផ} ቯ࿶ജḮߩ⺋▚ಽᏓࠍ㤥޿ᓇߩ㗔ၞߢ␜ߔޕ⺋Ꮕ▸࿐ ߪᐢߊޔᷓߐߪᶏᛮਅ_{1 㨪 8 km ߦ߽෸߱߇ޔ᳓ᐔ૏⟎} ߪࠞ࡞࠺࡜ർ✼ㇱ๟ㄝߢ޽ࠆߎߣ߇ࠊ߆ࠆޕ Fig. 6 ߦߪޔ࿶ജḮߩ૏⟎ߩઁޔFGS ࠍ࿕ቯߣߒߚฦ ᷹ὐ㧔ਣශ㧕ߦ߅ߌࠆ㊀ജᄌൻㅦᐲߣޔ࿶ജḮ߆ࠄᦼ ᓙߐࠇࠆ࿾⴫㕙ߦ߅ߌࠆ㊀ജᄌൻㅦᐲߩ㕙⊛ߥಽᏓ߽ ␜ߒߚޕᥦ⦡♽߇ᱜޔኙ⦡♽߇⽶ࠍ␜ߔޕ߹ߚޔ_{Fig. 7} ߦߪផቯߐࠇߚ࿶ജḮ߆ࠄߩ᳓ᐔ〒㔌ߦኻߔࠆ_{18 ᷹ὐ} ߩ㊀ജᄌൻㅦᐲߩ᷹ⷰ୯㧔⊕޿ࠪࡦࡏ࡞㧕ߣޔ⷗Ⓧ߽ ࠄࠇߚ࿶ജḮࡄ࡜ࡔ࡯࠲߆ࠄᦼᓙߐࠇࠆ⸘▚୯㧔㤥޿ ࠪࡦࡏ࡞㧕ࠍ␜ߔޕዪ࿾⊛ߦ㗼⪺ߥ࿾Ზᄌേ߇⍮ࠄࠇ ߡ޿ࠆߚ߼⸃ᨆߦߪ㒰ᄖߒߚޔਃේᣂጊ๟ㄝߩ᷹ὐ₄ ὐ㧔_{G05ޔG22ޔG24ޔG25㧕ߦߟ޿ߡ߽ෳ⠨ߩߚ߼ࡊࡠ࠶} ࠻ߒߚޕ

Table 3 Averaged gravity change rates with Std. Error (1σ) at the major stations except stations on and around Mt. Miharayama, referenced to FGS. GSI-FGS 2004/3/31 2009/ 6/26 96 0.0000 GSI-GOJINKACHAYA 2004/3/31 2008/ 7/28 11 -0.0057㫧0.0117 GSI-93051 2005/3/9 2009/ 6/23 7 -0.0021㫧_0.0041 GSI-93055 2005/10/26 2009/ 2/26 7 0.0097㫧0.0073 GSI-960594 2004/11/11 2009/ 6/23 11 -0.0019㫧_0.0029 GSI-960595 2005/10/26 2009/ 6/26 14 -0.0004㫧0.0035 ERI-ONSENHOTEL 2005/10/25 2009/ 6/21 10 -0.0152㫧_0.0055 ERI-O1003 2004/7/27 2009/ 6/21 7 -0.0086㫧0.0061 ERI-O1004 2004/7/27 2009/ 2/24 5 -0.0067㫧_0.0026 MRI-G01o 2004/11/11 2009/ 2/20 5 0.0053㫧_0.0034 MRI-G02 2005/10/27 2008/11/15 5 -0.0150㫧_0.0078 MRI-G03 2004/11/9 2009/ 6/21 8 -0.0061㫧_0.0043 MRI-G04 2004/11/10 2009/ 2/22 8 -0.0050㫧_0.0059 MRI-G11 2004/11/10 2009/ 6/23 11 -0.0101㫧_0.0062 MRI-G15 2005/3/11 2009/ 2/26 9 -0.0004㫧_0.0074 MRI-G16 2005/3/11 2009/ 6/23 7 0.0105㫧_0.0080 MRI-G17 2005/3/11 2009/ 2/26 9 0.0056㫧_0.0082 MRI-G18 2004/7/27 2009/ 6/21 9 -0.0128㫧_0.0071 MRI-G26 2004/11/11 2009/ 6/23 9 0.0021㫧_0.0035

Site Initial survey Last survey _{of measurements}Total number _{with Std. Error (1㱟) [mgal/Year]}Averaged gravity changes 気象研究所技術報告　第69号　2013

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㊀ജ᷹ⷰߦࠃࠅផቯߐࠇߚ࿶ജḮߪޔߎࠇ߹ߢ࿾Ზ ᄌേ᷹ⷰߢႎ๔ߐࠇߡ߈ߡ޿ࠆផቯ୯㧔଀߃߫ޔ㜞ᧁ࡮ ઁ㧔_{2008㧕ߢߪᷓߐ 5 kmޔ૕Ⓧᄌൻ㊂ 2 10}6_m3_/year㧕 ߣᲧߴࠆߣޔᷓߐߪ⚂_{1 km ᵻߊޔ᳓ᐔ૏⟎ߪ⧯ᐓ᧲ነ} ࠅߣߥߞߚ߇᭎ߨ৻⥌ߒߡ޿ࠆޕߒ߆ߒޔ૕Ⓧᄌൻ㊂_7.6 ₁₀6_m3_{/year ߪㆊᄢ⷗Ⓧ߽ࠅߐࠇߡ߅ࠅޔᷓߐߣߩ࠻} ࡟࡯࠼ࠝࡈ߽޽ࠆ߇_{4 ୚⒟ᐲᄢ߈޿ޕ㊀ജ᷹ⷰߦࠃࠆ} ⨃ᧁࡕ࠺࡞ࠍ઒ቯߒߚ࿶ജḮផቯ୯ߪޔᑼ㧔_{5㧕ࠍ⷗ߡ߽} ࠊ߆ࠆࠃ߁ߦޔ᜝ᒐౝߩ╙_{1 㗄ߩ਄ਅᄌേߦࠃࠆࡈ࡝࡯} ࠛࠕ࡯ߩነਈߦᄢ߈ߊᡰ㈩ߐࠇࠆޕߚߣ߃߫ޔ᜝ᒐౝ ╙_{2 㗄ߩ⃿ᲖౝኒᐲߩነਈߦᲧߴࠆߣޔ╙ 1 㗄ߩነਈ} ߪߘߩ㧙_{4 ୚એ਄ߣߥࠆ㧔ᑼ㧔6㧕㧕ޕ} E E E E E Q E S Q S f g g g C V G V C G f f ( ) . 0 1 2 0 0 3 4 3 4 4 13 㧔_6㧕 ߎߩߎߣߪޔ⧯ᐓᱜ⏕ߐࠍᰳߊ⴫⃻ߢߪ޽ࠆ߇ޔޟࡑࠣ ࡑ߇࿾ਅߩ⃿ᲖౝߦలႯߐࠇࠆߎߣߦࠃߞߡ᷹ⷰߐࠇ ࠆ㊀ജߩჇട㊂ࠃࠅ߽ޔ⤘ᒛߒߡ࿾⴫㕙߇㓉⿠ߔࠆߎ ߣߦࠃࠆ㊀ജߩᷫዋ㊂ߩᣇ߇_{4 ୚એ਄ᄢ߈޿ޠߎߣࠍ} ᗧ๧ߔࠆޕ FGS㧔ᄢፉ᷹୥ᚲ㧕ߢߪ GPS ㅪ⛯᷹ⷰࠍታᣉߒߡ޿ ࠆޕ߹ߚផቯ࿶ജḮߦᦨ߽ㄭ޿_{ONSENHOTEL ߦ߅޿} ߡ߽_{2007 ᐕ 3 ᦬߆ࠄ GPS ᷹ⷰࠍ㐿ᆎߒߚޕFGS ࠍ࿕} ቯߒߚ_{ONSENHOTEL ߩ㜞ߐߩ⋧ኻᄌൻࠍ Fig. 8 ߦ␜} ߔޕ᷹ⷰᦼ㑆ߪ_{2 ᐕ૛ࠅߦߔ߉ߥ޿߇ᐔဋ⊛ߥ㓉⿠ㅦ} ᐲߪ_{0.021 m/year ߢ޽ߞߚޕផቯߐࠇߚ࿶ജḮࡄ࡜ࡔ࡯} ࠲ࠍ↪޿ߡ_{ONSENHOTEL ߢᦼᓙߐࠇࠆ㓉⿠ㅦᐲࠍ⸘}

Fig. 5 Estimated pressure source based on the Mogi model us-ing gravity change rates referenced to FGS. An asterisk denotes an estimated source at a depth of 3.65 km. The shadowed and hatched area indicates the error

distribu-tion of the estimated source with 1σ standard deviadistribu-tion. Fig. 6 Estimated pressure source based on the Mogi model using gravity change rates referenced to FGS. An aster-isk denotes an estimated source at a depth of 3.65 km. Colored circles indicate observed gravity change rates according to the color palette. Color distribution on the land surface represents the calculated gravity change rate with estimated source parameters.

Fig. 7 Observed gravity change rates (open symbols) and calculated gravity change rates with estimated source parameters (solid symbols) including the four stations on and around Mt. Miharayama that were not used for source estimation.

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Relative Precise Gravity Survey at Izu-Oshima Volcano in the Eruption Preparation Period 2010 9

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㊀ജ᷹ⷰߦࠃࠅផቯߐࠇߚ࿶ജḮߪޔߎࠇ߹ߢ࿾Ზ ᄌേ᷹ⷰߢႎ๔ߐࠇߡ߈ߡ޿ࠆផቯ୯㧔଀߃߫ޔ㜞ᧁ࡮ ઁ㧔_{2008㧕ߢߪᷓߐ 5 kmޔ૕Ⓧᄌൻ㊂ 2 10}6_m3_/year㧕 ߣᲧߴࠆߣޔᷓߐߪ⚂_{1 km ᵻߊޔ᳓ᐔ૏⟎ߪ⧯ᐓ᧲ነ} ࠅߣߥߞߚ߇᭎ߨ৻⥌ߒߡ޿ࠆޕߒ߆ߒޔ૕Ⓧᄌൻ㊂_7.6 ₁₀6_m3_{/year ߪㆊᄢ⷗Ⓧ߽ࠅߐࠇߡ߅ࠅޔᷓߐߣߩ࠻} ࡟࡯࠼ࠝࡈ߽޽ࠆ߇_{4 ୚⒟ᐲᄢ߈޿ޕ㊀ജ᷹ⷰߦࠃࠆ} ⨃ᧁࡕ࠺࡞ࠍ઒ቯߒߚ࿶ജḮផቯ୯ߪޔᑼ㧔_{5㧕ࠍ⷗ߡ߽} ࠊ߆ࠆࠃ߁ߦޔ᜝ᒐౝߩ╙_{1 㗄ߩ਄ਅᄌേߦࠃࠆࡈ࡝࡯} ࠛࠕ࡯ߩነਈߦᄢ߈ߊᡰ㈩ߐࠇࠆޕߚߣ߃߫ޔ᜝ᒐౝ ╙_{2 㗄ߩ⃿ᲖౝኒᐲߩነਈߦᲧߴࠆߣޔ╙ 1 㗄ߩነਈ} ߪߘߩ㧙_{4 ୚એ਄ߣߥࠆ㧔ᑼ㧔6㧕㧕ޕ} E E E E E Q E S Q S f g g g C V G V C G f f ( ) . 0 1 2 0 0 3 4 3 4 4 13 㧔_6㧕 ߎߩߎߣߪޔ⧯ᐓᱜ⏕ߐࠍᰳߊ⴫⃻ߢߪ޽ࠆ߇ޔޟࡑࠣ ࡑ߇࿾ਅߩ⃿ᲖౝߦలႯߐࠇࠆߎߣߦࠃߞߡ᷹ⷰߐࠇ ࠆ㊀ജߩჇട㊂ࠃࠅ߽ޔ⤘ᒛߒߡ࿾⴫㕙߇㓉⿠ߔࠆߎ ߣߦࠃࠆ㊀ജߩᷫዋ㊂ߩᣇ߇_{4 ୚એ਄ᄢ߈޿ޠߎߣࠍ} ᗧ๧ߔࠆޕ FGS㧔ᄢፉ᷹୥ᚲ㧕ߢߪ GPS ㅪ⛯᷹ⷰࠍታᣉߒߡ޿ ࠆޕ߹ߚផቯ࿶ജḮߦᦨ߽ㄭ޿_{ONSENHOTEL ߦ߅޿} ߡ߽_{2007 ᐕ 3 ᦬߆ࠄ GPS ᷹ⷰࠍ㐿ᆎߒߚޕFGS ࠍ࿕} ቯߒߚ_{ONSENHOTEL ߩ㜞ߐߩ⋧ኻᄌൻࠍ Fig. 8 ߦ␜} ߔޕ᷹ⷰᦼ㑆ߪ_{2 ᐕ૛ࠅߦߔ߉ߥ޿߇ᐔဋ⊛ߥ㓉⿠ㅦ} ᐲߪ_{0.021 m/year ߢ޽ߞߚޕផቯߐࠇߚ࿶ജḮࡄ࡜ࡔ࡯} ࠲ࠍ↪޿ߡ_{ONSENHOTEL ߢᦼᓙߐࠇࠆ㓉⿠ㅦᐲࠍ⸘}

Fig. 5 Estimated pressure source based on the Mogi model us-ing gravity change rates referenced to FGS. An asterisk denotes an estimated source at a depth of 3.65 km. The shadowed and hatched area indicates the error

distribu-tion of the estimated source with 1σ standard deviadistribu-tion. Fig. 6 Estimated pressure source based on the Mogi model using gravity change rates referenced to FGS. An aster-isk denotes an estimated source at a depth of 3.65 km. Colored circles indicate observed gravity change rates according to the color palette. Color distribution on the land surface represents the calculated gravity change rate with estimated source parameters.

Fig. 7 Observed gravity change rates (open symbols) and calculated gravity change rates with estimated source parameters (solid symbols) including the four stations on and around Mt. Miharayama that were not used for source estimation.

10 ▚ߔࠆߣ_{0.103 m/year ߣߥࠅޔGPS ߢ᷹ⷰߐࠇߚ㊂ߩ} ⚂_{5 ୚ߣ޿߁ᄢ߈ߥ㊂ߣߥࠆޕ઒ߦផቯߐࠇߚ૕Ⓧᄌ} ൻ㊂߇_{5 ୚⒟ᐲㆊᄢ⷗Ⓧ߽ࠅߐࠇߡ޿ࠆߣ⠨߃ࠆߣޔ} EV ߪផቯߐࠇߚᄢ߈ߐߩ1/5 ⒟ᐲ߇߽ߞߣ߽ࠄߒ޿ߣ ផ᷹ߐࠇࠆޕ ᑼ㧔_{7㧕ߪᑼ㧔5㧕ߩ৻ㇱࠍᄌᒻߒߚ߽ߩߢ޽ࠆޕ} E Q S E g C G V D r D f «¬®® ®® º » ®® ¼®® 3 4 0 ₍ 2 2 3 2₎/ 㧔7㧕 ਛ᜝ᒐౝ╙_{1 㗄߇ࡈ࡝࡯ࠛࠕ࡯ߩነਈ㗄ޔ╙ 2 㗄߇} ⃿Ზౝߩኒᐲߩነਈ㗄ߢ޽ࠆޕ_{EV ࠍ}_{1/5 ߣߒߚ߁߃ߢޔ} ㊀ജ᷹ⷰߢᓧࠄࠇߚ㊂_{E g ࠍ⺑᣿ߔࠆߎߣߪน⢻ߢ޽ࠈ} ߁߆ޕ_S₀_{= 2.67 10}3_kg/m3ߩ႐วߩ᜝ᒐౝߩੑ㗄ߩᲧ ߪ㧙_{4㧦1 ߢ޽ߞߚ㧔ᑼ㧔6㧕㧕ޕEV ࠍ 1/5 ߣߒߚ႐วߦߪޔ} ߘߩᲧࠍ㧙_{4㧦㧙11 ߣߔࠇ߫ᑼ㧔7㧕ߩ Eg ࠍ⺑᣿ߔࠆߎ} ߣ߇น⢻ߦߥࠆޕߎߩߎߣߪ_S₀ߩ_{11 ୚ߩኒᐲߩ‛⾰} ߇ᶖᄬߒޔߒ߆߽⤘ᒛߔࠆߣ޿߁ߎߣߦߥࠆ߇ޔߎࠇ ߪ⃻ታ⊛ߢߪߥ޿ޕ ᵴേ⊛ߥἫጊߢߪἫጊᕈߩ⣕ࠟࠬᵴേߦࠃߞߡࡑࠣ ࡑߩ⾰㊂߇ᷫዋߔࠆޕ઒ߦ⣕ࠟࠬߦࠃߞߡޔ೨ㅀߩޟ_S₀ ߩ_{11 ୚ߩኒᐲߩ‛⾰߇ᶖᄬߒߚߎߣޠߣ╬ଔߥߎߣ߇} ࿾ਅߩ࿶ജḮઃㄭߢ⿠ߎߞߡ޿ࠆߣ઒ቯߒߡࠟࠬߩ᡼ ಴࡟࡯࠻ࠍ⸘▚ߔࠆߣޔߘߩ㊂ߪ_{4.5 10}10_{kg/year ߣ} ߥࠆޕᣣ឵▚ߢ_{120,000 ton/day ߢ޽ࠅޔߎߩ㊂ߪਃቛ} ፉ_{2000 ᐕྃἫᓟߩᦨ⋓ᦼߩੑ㉄ൻ⎫㤛ࠟࠬߩྃ಴࡟࡯} ࠻ߦ඘ᢜߔࠆ㧔_{Kazahaya et al., 2004㧕ޕ㗼⪺ߥ⣕ࠟࠬᵴ} േߩ޽ߞߚਃቛፉߢߪߘࠇߦ઻߁ጊ૕ߩ෼❗ࠍ઻ߞߡ ޿ߚޕ߹ߚદ⼺ᄢፉߢߪྃᾍᵴേߪૐ⺞ߢ޽ࠅޔ⣕ࠟ ࠬߢ㊀ജ࠺࡯࠲ߣ㓉⿠࠺࡯࠲ࠍ⺑᣿ߔࠆߎߣߪ࿎㔍ߢ ޽ࠆޕ દ⼺ᄢፉߢߪޔ_{1986 ᐕྃἫએ೨ߦ߽➅ࠅ㄰ߒ㊀ജⷰ} ᷹ߩ޿ߊߟ߆ߩ⚿ᨐ߇ႎ๔ߐࠇߡ޿ࠆޕߎࠇࠄߪޔ⍴ ᦼ㑆⊛ߥ଀ᄖߪ޽ࠆ߽ߩߩ㧔੗਄࡮ઁ_{, 1972㧕ޔ߅߅} ߻ߨ⚻ᐕ⊛ߦౝ㒽ㇱߩ㊀ജ୯ߪ⋧ኻ⊛ߦᷫዋߒߡ޿ࠆ ߣ޿߁᷹ⷰ⚿ᨐߢ޽ࠆޕዊᴰ࡮ઁ㧔_{1986㧕ߦࠃࠆߣޔ} 1979 ᐕ߆ࠄ 1985 ᐕߩ᷹ⷰ୯ߪፉߩ๟✼ߦᲧߴߡౝ㒽ㇱߢ⋧ኻ⊛ߦ㊀ജ୯߇ᷫዋߒߡ޿ࠆߎߣࠍႎ๔ߒߡ޿ ࠆޕ଀߃߫ࠞ࡞࠺࡜ઃㄭ㧔ᧄႎ๔ߩ_{GOJINKACHAYA㧕} ߢߪ_{0.12 mgal ߽ߩᷫዋ߇᷹ⷰߐࠇߚޕߎߩ㊀ജᄌൻㅦ} ᐲߪޔᚒޘߩ᷹ⷰ⚿ᨐߣห⒟ᐲߢ޽ࠆޕߚߛߒߎࠇࠄ ߩႎ๔ߢߪޔ㜞ߐߩᄌൻߦߟ޿ߡߩ᷹ⷰᚑᨐߦߟ޿ߡ ߪ⸅ࠇࠄࠇߡ޿ߥ޿ޕ ߎߩࠃ߁ߦޔౝ㒽ㇱߢᦨᄢ_{0.015 mgal/year ⒟ᐲߩ㊀} ജᷫዋߪ_{1986 ᐕྃἫએ೨߆ࠄ⃻࿷߹ߢ⛮⛯⊛ߦ⷗ࠄࠇ} ߡ޿ࠆ߇ޔߎࠇߦ⷗ว߁㓉⿠㊂ߪ᷹ⷰߐࠇߡ޿ߥ޿ޕ ߎߩߎߣߪޔદ⼺ᄢፉߩ࿾Ზᄌേ߿㊀ജᄌൻߪޔන৻ ࿶ജḮ߿ᒢᕈ⊛ߥᝄࠆ⥰޿ߢ⺑᣿ߔࠆࠃࠅ߽೎ߩⶄ㔀 ߥࡔࠞ࠾࠭ࡓߢ⺑᣿ߔࠆߎߣࠍᬌ⸛ߔࠆᔅⷐᕈࠍ␜ໂ ߔࠆޕߎߩߚ߼ߦߪޔᦝߦ♖ኒߥ㊀ജ࠺࡯࠲ߩ⫾Ⓧߩ ઁߦޔ㜞♖ᐲߩ㜞ߐᄌൻߩ࠺࡯࠲⫾Ⓧࠍᓙߚߥߌࠇ߫ ߥࠄߥ޿ޕ

6㧚߹ߣ߼

દ⼺ᄢፉߩྃἫḰ஻ᦼߦ߅ߌࠆࡑࠣࡑ⫾Ⓧㆊ⒟ࠍ⍮ ࠆߚ߼ߩ߭ߣߟߩᚻᲑߣߒߡޔ_{2004 ᐕ߆ࠄ 2009 ᐕߩ} 㑆ߦ_{14 ࿁ߩ⋧ኻ㊀ജ᷹ⷰࠍታᣉߒߚޕߘߩ⚿ᨐޔࠞ࡞} ࠺࡜ർㇱࠍਛᔃߦᦨᄢߢ_{0.015 mgal/year ߩ⋧ኻ⊛ߥ㊀} ജ୯ߩᷫዋ߇⷗ࠄࠇߚޕ⨃ᧁࡕ࠺࡞ࠍ઒ቯߒߡ࿶ജḮ ࠍផቯߒߚߣߎࠈޔᶏᛮਅ_{3.65 km ߢ 7.6 10}6_m3_/year ߩ૕Ⓧ⤘ᒛ߇޽ࠇ߫⺑᣿ߢ߈ࠆߎߣ߇ࠊ߆ߞߚޕߒ߆ ߒޔߎߩ࿶ജḮࡄ࡜ࡔ࡯࠲ߢᦼᓙߐࠇࠆ࿾⴫ߩ㓉⿠㊂ ߪ_{GPS ߢ᷹ⷰߐࠇߚ⚿ᨐࠃࠅ߽ 5 ୚߽ᄢ߈ߊޔ㊀ജᄌ} ൻߣ࿾Ზᄌേࠍหᤨߦ⺑᣿ߔࠆߎߣߪߢ߈ߥ޿ޕ߹ߚ ࿶ജḮ⃿Ზౝߩኒᐲߩ⸳ቯߩ઀ᣇߢኻᔕߢ߈ࠆ▸࿐߆ ࠄㅺ⣕ߒߡ޿ߚޕ ߎߩࠃ߁ߥ㊀ജᄌൻ㊂ಽᏓߪ_{1986 ᐕྃἫએ೨ߦ߽ႎ} ๔ߐࠇߡ޿ࠆޕ᷹ⷰߐࠇߚ㊀ജᄌൻಽᏓߣߘࠇߦၮߠ ޿ߡផቯߐࠇߚࡑࠣࡑ⫾Ⓧㅦᐲ߇ᱜߒ޿ߣߔࠇ߫ޔⷰ ᷹ߐࠇߚ㓉⿠ㅦᐲߪ⫾Ⓧㅦᐲ߆ࠄᦼᓙߐࠇࠆ㊂ࠍ⺑᣿ ߢ߈ߥ޿ޕߎߩߎߣߪޔદ⼺ᄢፉߪ࿾Ზᄌേ߿㊀ജᄌ ൻࠍන৻࿶ജḮ߿ᒢᕈ⊛ߥᝄࠆ⥰޿ߢ⺑᣿ߔࠆߎߣ߇ ࿎㔍ߥޔࡑࠣࡑ⫾Ⓧㆊ⒟ߩⶄ㔀ߥἫጊߢ޽ࠆߎߣࠍ␜ ໂߔࠆߩ߆߽ߒࠇߥ޿ޕߎࠇࠄࠍ⸃᣿ߔࠆߚ߼ߦߪޔ ᦝߦ♖ᐲߩ㜞޿㊀ജ᷹ⷰ࠺࡯࠲ޔ෸᷹߮࿾࠺࡯࠲ߩ⫾ Ⓧ߇੹ᓟ߽ᔅⷐߢ޽ࠆޕ

⻢ㄉ

ᧄ᷹ⷰߢߪᄙߊߩᣇߩදജࠍᓧߡⴕࠊࠇߚޕ቟⮮ᔋ ᳁ޔဈ੗ቁⴕ᳁ޔᣂၳᢅၮ᳁ޔጊᧄື਽᳁ޔ㤥ᧁ⧷Ꮊ᳁ޔ ᵻᴧశノ᳁ߦߪ᷹ⷰߦߏදജ㗂޿ߚޕ߹ߚᄢፉ᷹୥ᚲ ߩᄙߊߩ⡯ຬߦߪో㕙⊛ߦᡰេߒߡ㗂޿ߚޕ࿖࿯࿾ℂ 㒮ߦߪ㔚ሶၮḰὐޔ㊀ജὐޔ᳓Ḱὐࠍ೑↪ߐߖߡ㗂޿ ߚޕ᧲੩ᄢቇ࿾㔡⎇ⓥᚲߦߪၮḰὐࠍ೑↪ߐߖߡ㗂޿ ߚޕᄢፉ↸෸߮ᄢፉ⼊ኤ⟑ߦߪޔࠞ࡞࠺࡜ౝߦ߅ߌࠆ ᷹ⷰߦߏ㈩ᘦࠍ㗂޿ߚޕ߹ߚޔ_{2 ฬߩඞฬߩᩏ⺒⠪ߩ} ᑪ⸳⊛ߥߏᗧ⷗ߦࠃࠅޔᧄⓂߪᄢ߈ߊᡷༀߐࠇߚޕ✬ 㓸ᆔຬߩᨋ⼾᳁ߦߪ᦭ᗧ⟵ߥߏᜰ៰ࠍ㗂޿ߚޕߎߎߦ ⸥ߒߡߺߥߐ߹߳ᗵ⻢ߩᗧࠍ⴫ߒ߹ߔޕ

Fig. 8 Temporal altitude change at ONSENHOTEL station ref-erenced to FGS by GPS observation. Averaged altitude change rate is 0.021 m/year.

62

63

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ෳ⠨ᢥ₂

Carbone, D., G. Currenti and C. Del Negro, 2007: Elastic model for the gravity and elevation changes before the 2001 eruption of Etna volcano, Bull Volcanol, 69, 553-562.

⑔੗ᢘ৻࡮ဈ੗ቁⴕ࡮ጊᧄື਽࡮⮮ේஜᴦ࡮㜞ᧁᦶల࡮ਛ⑥ᱜ᣿, 2003: ᮡ㜞⵬ᱜ⨃ᧁࡕ࠺࡞ߩ᦭↪ᕈߣߘߩ㒢⇇, ᣣᧄἫጊ ቇળ⻠Ṷ੍Ⓜ㓸_{, 35.} ฎደᱜੱ࡮ᄢਭ଻ୃᐔ࡮↰ਛᗲᐘ࡮ቊޓᢥ⑼࡮ᷰㄝ⑲ᢥ࡮෸ Ꮉޓ⚐࡮೨Ꮉᓼశ, 2001: ㊀ജߩᤨⓨ㑆ᄌൻߢߣࠄ߃ߚਃ ቛፉ2000 ᐕἫጊᵴേߦ߅ߌࠆࠞ࡞࠺࡜ᒻᚑㆊ⒟, ࿾ቇ㔀 ⹹_{, 110, 2, 217-225.} ⪤ේᐘ↵, 1977: દ⼺ඨፉߩ⇣Ᏹ㓉⿠ࠍ⺑᣿ߔࠆ⨃ᧁࡕ࠺࡞ ߣ ߘ ࠇ ߦ ઻ ߁ ㊀ ജ ᄌൻ, ᧲੩ᄢቇ࿾㔡⎇ⓥᚲᒵႎ, 52, 301-309. ੗ౝޓ⊓࡮ട⚊సᏈ࡮⮮੗㓁৻㇢, 1972: ᄢፉߦ߅ߌࠆ㊀ജᄌ ൻߩ⎇ⓥ㧔II㧕, ᷹࿾ቇળ, 18, 104-111.

Jentzsch, G., R. Punongbayan, U. Schreiber, G. Seeber, C. Volksen and A. Weise, 2001: Mayon volcano, Philippines: change of monitoring strategy after microgravity and GPS measurements from 1992 to 1996, J. Volcano. Geotherm. Res., 109, 219-234. Jousset, P., H. Mori and H. Okada, 2003: Elastic models for the

magma intrusion associated with the 2000 eruption of Usu Volcano, Hokkaido, Japan, J. Volcano. Geotherm. Res., 125, 81-106.

Ꮉㄝ⑓ਭ, 1991: દ⼺ᄢፉἫጊߩጤ⍹ቇ⊛⊒㆐ผ, Ἣጊ, 36, 297- 310.

Kazahaya, K., H. Shinohara, K. Uto, M. Odai, Y. Nakahori, H. Mori, H. Iino, M. Miyashita and J. Hirabayashi, 2004: Gigantic SO2 emission from Miyakejima volcano, Japan, caused by caldera collapse, Geology, 32, 5, 425-428. ዊᴰጪม࡮⑔੗ᢘ৻࡮ᯅᧄᔀᄦ࡮ᐓ႐లਯ࡮ᷡ㊁᡽᣿࡮㉿᧛ᐙᄦ, 1988: દ⼺ᄢፉߦ߅ߌࠆ㊀ജᄌൻ г 1985 ᐕ 11 ᦬㨪1988 ᐕ 5 ᦬г, Ἣጊ, 33, 291-303. ዊᴰጪม࡮ศ↰᣿ᄦ࡮⍹Ꮉ᦭ਃ࡮Ỉ↰นᵗ࡮੗ౝޓ⊓, 1986: દ⼺ᄢፉߦ߅ߌࠆ㊀ജ᷹ቯг1985 ᐕ 11 ᦬г, ᳇⽎⎇ⓥᚲ⎇ ⓥႎ๔, 37, 271-280.

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Tamura, Y., 1982: A computer program for calculating the tide-generating force, Publ. Int. Latit. Obs. Mizusawa, 16, 1-20. ᷰㄝ⑲ᢥ࡮ᄢਭ଻ୃᐔ࡮ဈਅ⥋ഞ, 1990: 㒠᳓ߩ㊀ജߦ߅ࠃ߷ ߔᓇ㗀⹏ଔ 㧙 ᜛ᢔࡕ࠺࡞, ᣣᧄἫጊቇળ⑺ቄ⻠Ṷ੍Ⓜ㓸, 56. ጊᧄ࿻๋࡮㜞ጊ㋕ᦶ࡮⍹ේ๺ᒄ࡮ᄢፉᒄశ࡮೨Ꮉᓼశ࡮ᬀᧁ⽵ੱ࡮ ᴛ↰ቬਭ࡮෸Ꮉޓ⚐, 1998: ᪉ፉ߅ࠃ߮ᆨ⦟ࠞ࡞࠺࡜๟ ㄝߦ߅ߌࠆ㊀ജᄌൻ, ੩ㇺᄢቇ㒐ἴ⎇ⓥᚲᐕႎ, 41B-1, 153-160.

ྃἫḰ஻ᦼߦ߅ߌࠆદ⼺ᄢፉߩ⋧ኻ♖ኒ㊀ജ᷹ቯ

㜞ᧁᦶల

_{࡮⑔੗ᢘ৻࡮ጊ㉿ޓᐔ㧔᳇⽎⎇ⓥᚲ࿾㔡Ἣጊ⎇ⓥㇱ㧕}

ޓޓޓ ⮮ේஜᴦ

_{㧔ᄢ㒋▤඙᳇⽎บ㧕}

ടᴦደ⑺ታ

_{㧔ᄢፉ᷹୥ᚲ㧕}

ྃἫḰ஻ᦼߦ߅ߌࠆદ⼺ᄢፉἫጊߩࡑࠣࡑ⫾Ⓧㆊ⒟ࠍ᣿ࠄ߆ߦߔࠆߚ߼ޔ2004 ᐕ߆ࠄ 2009 ᐕߦ 14 ࿁ߩ⋧ኻ♖ኒ㊀ജ᷹ቯ ߇ߥߐࠇߚޕ㊀ജᄌൻߪጊ㗂ࠞ࡞࠺࡜ർ✼ࠍਛᔃߦᷫዋߔࠆ௑ะߢ޽ࠅޔ㊀ജᷫዋㅦᐲߪᦨᄢߢ0.015 mgal/year ߢ޽ߞߚޕ⨃ ᧁࡕ࠺࡞ࠍ઒ቯߒߡ࿶ജḮࡄ࡜ࡔ࡯࠲ࠍ᳞߼ࠆߣޔ᷹ⷰ࠺࡯࠲ࠍ⺑᣿ߢ߈ࠆࡄ࡜ࡔ࡯࠲ߣߒߡޔ7.6 106_m3_{/year ߩ૕Ⓧ⤘ᒛ} ߔࠆᶏᛮਅ3.65 km ߩᷓߐߩ࿶ജ⤘ᒛḮ߇⷗Ⓧ߽ࠄࠇߚޕߒ߆ߒ⷗Ⓧ߽ࠄࠇߚ૕Ⓧ⤘ᒛ߆ࠄ⸘▚ߐࠇࠆ㓉⿠ㅦᐲߪ GPS ߦࠃࠆ ᷹ⷰ୯ߩ5 ୚ߦ߽ߥࠅޔߎࠇࠄ⷗Ⓧ߽ࠄࠇߚ⤘ᒛḮߩࡄ࡜ࡔ࡯࠲ߪޔ㊀ജߣ㓉⿠ߩᄌൻࠍหᤨߦߪ⺑᣿ߔࠆߎߣߪߢ߈ߥ޿ޕ દ⼺ᄢፉἫጊߪන⚐ߥ‛ℂࡕ࠺࡞ߢ␜ߔߎߣ߇ߢ߈ߥ޿ⶄ㔀ߥࡑࠣࡑ⫾Ⓧ♽ࠍ᦭ߔࠆἫጊߢ޽ࠆߩ߆߽ߒࠇߥ޿ޕߎߩࠃ߁ ߥⶄ㔀ߥἫጊߩࡑࠣࡑ⫾Ⓧ♽ࠍ᣿ࠄ߆ߦߔࠆߚ߼ߦߪޔ㓉⿠㊂ߩ᷹ⷰߣߣ߽ߦߐࠄߥࠆ㜞♖ᐲߩᓸዊ㊀ജ᷹ⷰࠍ੹ᓟ߽⛮⛯ߔ ࠆᔅⷐ߇޽ࠆޕ * ⃻ᚲዻ㧦ᢥㇱ⑼ቇ⋭ ⎇ⓥ㐿⊒ዪ ࿾㔡࡮㒐ἴ⎇ⓥ⺖ ** ⃻ᚲዻ㧦᳇⽎ᐡ࿾㔡ἫጊㇱἫጊ⺖