| 講演要旨(和文) | | 秋田駒ケ岳火山における重力変化の特徴を熱活動との関わりでモデル化する．噴火終息後，火口周辺域で地温が高まった.それは1977-80年頃を最大として，以後漸次低下し，1998年頃までにはほぼ完全に減退した．観測重力値は1977年から1998年までの期間に著しく増加した．このことはこの地域の熱活動と密接に関連しているようである．本論文では，重力減少を大地の熱膨張によって説明するモデルを提示する．モデルは表面直下に(1)半球状や(2)半無限円柱状などの特定領域を持つ半無限等方均質弾性体である．領域内温度を一様と仮定して，その温度増加による熱膨張の影響を数学的に評価する．結局, 熱膨張は地表面の隆起と密度の減少をもたらす．重力は主として前者により，部分的には後者によって減少する．観測現象はほぼこのモデルで説明されるように思われる． |
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| | 講演要旨(英文) | | Characteristic changes of gravity at Akita-Komagatake Volcano after the eruption of 1970 are proposed to model with thermal activity in the area. After the eruption, ground temperature in surrounding area of the crater increased and reached the maximum peak during 1977-80 and then decreased and decayed almost completely until 1998. The observed gravities considerably increased in the period from 1977 to 1998. This fact is very likely to be connected with thermal activity in the area. In this paper a model is proposed to explain the decrease of gravity by the thermal expansion of the ground. The model consists of a semi-infinite isotropic homogeneous medium with a particular zone of (1) semi-sphere or (2) semi-infinite cylinder immediately under the surface. Effects of thermal expansion by increase of the temperature in the zone are mathematically evaluated assuming the constant temperature in the zone. The results show that the thermal expansion causes rise of the ground surface and decrease of density. Gravity on the ground surface is decreased mainly by the former and partly by the latter. Observed phenomena are considered as explained almost by this model. |
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