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Bernard A. Chouet

Publications and source records attributed to Bernard A. Chouet.

23 records · Page 2Linked to original sources
USGS2004

Pressure changes associated with the ascent and bursting of gas slugs in liquid-filled vertical and inclined conduits

At basaltic volcanoes, the sources of long-period and very-long-period seismicity and acoustic signals are frequently described in terms of fluid dynamic processes, in particular the formation and ascent of gas slugs within the magma column and their bursting at the surface. To investigate pressure changes associated with these processes, two-phase flow experiments have been carried out in vertical and inclined pipes with both single gas slugs and a continuously supplied gas phase. The ascent of individual gas slugs is accompanied by strong dynamic pressure variations resulting from the flow of liquid around the slug. These dynamic transients generate sub-static pressures below the ascending slug in viscosity-controlled systems, and produce super-static pressures when the slug reaches the surface and motion ceases in inertia-dominated systems. Conduit inclination promotes a change of regime from bubbly to slug flow and favours an increase in size and velocity of the slugs at the expense of their frequency of occurrence during continuously supplied two-phase flow. The experimental pressure data support previous theoretical analyses of oscillatory sources in ascending slugs as the slugs approach the surface and burst. Pressure oscillations are also observed during the release of gas slugs and in their wake region.

Journal of Volcanology and Geothermal Research↗
USGS2002

Analysis of long-period events recorded at Mount Etna (Italy) in 1992, and their relationship to eruptive activity

Seismic activity recorded at Mount Etna during 1992 was characterized by long-period (LP) events and tremor with fluctuating amplitudes. These signals were associated with the evolution of the eruptive activity that began on December 14, 1991. Following the occurrence of numerous volcano-tectonic earthquakes at the onset of the eruption, LP events dominated the overall seismicity starting in January, 1992. The LP activity occurred primarily in swarms, which were temporally correlated with episodic collapses of the crater floor in the Northeast Crater. Source depths determined for selected LP events suggest a source region located slightly east of Northeast Crater and extending from the surface to a depth of 2000 m. Based on the characteristic signatures of the time series, four families of LP events are identified. Each family shares common spectral peaks independent of azimuth and distance to the source. These spectral features are used to develop a fluid-filled crack model of the source. We hypothesize that the locus of the LP events represents a segment of the magma feeding system connecting a depressurizing magma body with a dike extending in the SSE direction along the western wall of Valle del Bove, toward the site of the Mount Etna eruption. We surmise that magma withdrawal from the source volume beneath Northeast Crater may have caused repeated collapses of the crater floor. Some collapse events may have produced pressure transients in the subjacent dike which acted as seismic wave sources for LP events.

Mount Etna, Sicily↗
USGS1997

Imaging the crustal magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii

Three-dimensional seismic P-wave traveltime tomography is used to image the magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii. High-velocity bodies (>6.4 km/s) in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro-ultramafic cumulates from which the surface volcanism is derived. The proximity of these high-velocity features to the rift zones is consistent with a ridge-spreading model of the volcanic flank. Southeast of the Hilina fault zone, along the south flank of Kilauea, low-velocity material (<6.0 km/s) is observed extending to depths of 9–11 km, indicating that the Hilina fault may extend possibly as deep as the basal decollement. Along the southeast flank of Mauna Loa, a similar low-velocity zone associated with the Kaoiki fault zone is observed extending to depths of 6–8 km. These two upper crustal low-velocity zones suggest common stages in the evolution of the Hawaiian shield volcanoes in which these fault systems are formed as a result of upper crustal deformation in response to magma injection within the volcanic edifice.

Geology↗
USGS1996

Long-period volcano seismicity: Its source and use in eruption forecasting

At an active volcano, long-period seismicity (with typical periods in the range 0.2–2 s) reflects pressure fluctuations resulting from unsteady mass transport in the sub-surface plumbing system, and hence provides a glimpse of the internal dynamics of the volcanic edifice. When this activity occurs at shallow depths, it may signal the pressure-induced disruption of the steam-dominated region of the volcano, and can accordingly be a useful indicator of impending eruption.

Nature↗