B36 Source Model of Volcanic explosions constrained by seismic and infrasonic time delays

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概要

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• An explosive source mechanism, which characterizes the volcanic activity of Stromboli, is analyzed by seismic and infrasonic measurements correlated to digitally processed images of the explosive events (fig. 1). Infrasonic records associated with short-period seismic signals give evidence that the high-frequency (>5 Hz) wavefield is produced by a seismic source which is coupled to the atmosphere (fig. 1B). The time delay between seismic (fig. 1A) and infrasonic onsets (fig. 1B) is not stable and the fluctuations could reflect a change in the magma-gas physical properties, and indicates (fig. 2) that source dynamics in magma involves low velocities (<100 m/s). Time delays (0.5-1.3 s) between infrasonud and visible explosive onset (fig. 1C) indicates that gas fragments mixture is moving with subsonic velocity (<700 m/s) in the conduit above the magma free surface. A foam collapse model (fig. 3) has been checked in laboratory experiments by recording acoustic signals produced during gas bubbles growth, flow and burst in a liquid. The observed signals (fig.4) present strong similarities to short-period (>1s) as well as broadband (10-1 s) seismic signals recorded at Stromboli. Low frequency rarefaction is observed when the foam collapse occurs and the gas bubble starts to rise up along the pipe (T1,fig. 4), then an audible sound is emitted by the bubble film breaking at the liquid free surface (T2,fig. 4). By analogy, we infer that low frequency seismic decompression is generated by the rapid expansion of gas in the magma conduit (fig. 3B), while high frequency seismic signal and infrasound, are generated by the explosion at the magma free-surface (fig. 3D). Assuming the foam collapse model, we calculate that seismic signal is produced by gas expansion of ≈30 m^3 which induces a pressure drop of ≈0.1 MPa. Infrasonic waves are generated by an gas overpressure of ≈2×(10)^5 Pa.

• 特定非営利活動法人日本火山学会の論文
• 2000-09-30

著者

• Ripepe M.

  Dipartimento Di Scienze Della Terra Universita'di Firenze:institute Of Seismology And Volcanolo

• Ciliberto S.

  Ecole Normale Superieure de Physique

• Della Schiava

  Dipartimento di Scienze della Terra, Universita'di Firenze

• Della Schiava

  Dipartimento Di Scienze Della Terra Universita'di Firenze

関連論文

• B36 Source Model of Volcanic explosions constrained by seismic and infrasonic time delays

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