Free oscillations of a fluid sphere in an infinite elastic medium and long-period volcanic earthquakes.
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Accession number;02A0283556
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| Title;Free oscillations of a fluid sphere in an infinite elastic medium and long-period volcanic earthquakes. |
| Author;
SAKURABA A
(Univ. Tokyo, Tokyo, Jpn)
OIKAWA J
(Univ. Tokyo, Tokyo, Jpn)
IMANISHI Y
(Univ. Tokyo, Tokyo, Jpn)
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Journal Title;Earth, Planets Space
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Journal Code:G0106B
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ISSN:1343-8832
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VOL.54;NO.2;PAGE.91-106(2002)
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| Figure&Table&Reference;FIG.19, TBL.2, REF.18 |
| Pub. Country;Japan |
| Language;English |
| Abstract;A source model of long-period volcanic earthquakes is presented. We consider that a fluid-filled spherical cavity surrounded by an infinite elastic medium is excited into resonance like the Earth's free oscillations. The eigenequation of this system is derived in a general manner, making use of the spherical harmonic and spherical Bessel expansions. The solution is given as a complex number; its real part is the eigenfrequency and the imaginary part represents the attenuation coefficient of the oscillation. The eigenmodes are classified into five groups: (1) the compressional modes in a fluid sphere, (2) the compressional modes in a solid medium, (3) the shear modes in a solid medium, (4) the Stoneley modes, and (5) the torsional modes. We apply them to the long-period volcanic earthquake observed at Asama volcano, Japan. Estimating the characteristic frequencies and attenuation coefficients of the observed vibrations and assuming that the primary component (f = 1.73 Hz) corresponds to the fundamental translation mode of a fluid sphere as one of the compressional modes in fluid, we conclude that the resonator which is a spherical cavity of diameter 220 m filled with steam of temperature 500.DEG.C. and pressure 170 atm is favorable. (author abst.) |
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