Seismicity associated with renewed dome building at Mount St. Helens, 2004-2005

Morgan, Seth C.; Malone, Stephen D.; Qamar, Anthony; Thelen, W. A.; Wright, Amy; Caplan‐Auerbach, J.

doi:10.3133/pp17502

Cited by 71 publications

(107 citation statements)

References 14 publications

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“…Initial seismicity consisted largely of volcano-tectonic (VT) earthquakes but soon transitioned to low-frequency (LF) and hybrid events (those with a high-frequency onset but transitioning to lower frequencies), following a pattern observed at many dome-building eruptions [Moran et al, 2008a] including at MSH in the 1980s. Earthquakes were mostly located <1 km below the crater floor, and very early in the eruption exhibited temporal shallowing on a north dipping structure likely coincident with the shallow conduit [Thelen et al, 2008].…”

Section: The 2004-2008 Eruption Of Mount St Helensmentioning

confidence: 99%

“…This event excavated a large horseshoe-shaped crater in which domeforming eruptions continued until 1986. After nearly 20 years of quiescence, and following only a few days of increased seismic activity [Moran et al, 2008a] [Vallance et al, 2008]. The growth rate of the dome declined quasi-exponentially from ∼8 m 3 /s S.…”

Section: The 2004-2008 Eruption Of Mount St Helensmentioning

confidence: 99%

“…Drumbeats occurred roughly every 1 min during the early part of the eruption, but repeat times increased and drumbeats nearly vanished by August 2005. They reappeared in October 2005 (close to the time of the first tiltmeter installation) with a recurrence interval of about 70 s [Moran et al, 2008a], but became less common through 2006, and in 2007 were too irregularly spaced to warrant the term drumbeat (although they shared many other characteristics of the drumbeats) (S. Moran, personal communication, 2009). Finally, a small number of drumbeats were associated with the very end of the eruption in 2008 (S. Moran, personal communication, 2009).…”

Section: Lf and Hybrid Earthquakesmentioning

confidence: 99%

“…These events shared several characteristics with the drumbeats including an LF or hybrid nature and tendency to exhibit down first motions on most seismic stations. They may have been related to lurching of the active spine, and may have occurred at the boundary between the base of the spine and the 1980s crater floor [Moran et al, 2008a].…”

Section: > > > > > > > > > > > > > > > 2 Earthquakesmentioning

confidence: 99%

“…[9] More than one million shallow earthquakes were recorded at MSH between the onset of the eruption and the end of 2005 [Moran et al, 2008a;Thelen et al, 2008]. Initial seismicity consisted largely of volcano-tectonic (VT) earthquakes but soon transitioned to low-frequency (LF) and hybrid events (those with a high-frequency onset but transitioning to lower frequencies), following a pattern observed at many dome-building eruptions [Moran et al, 2008a] including at MSH in the 1980s.…”

Section: The 2004-2008 Eruption Of Mount St Helensmentioning

confidence: 99%

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Cyclic ground tilt associated with the 2004–2008 eruption of Mount St. Helens

2010

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[1] The long-term behavior of the 2004-2008 effusive eruption of Mount St. Helens was characterized by a gradual decline in the rates of seismicity, dome growth, and broad-scale ground deformation, but shallow near-periodic "drumbeat" earthquakes over timescales of minutes indicated episodic short-term behavior. In part to better characterize this behavior and any associated ground deformation, a network of tiltmeters was installed and recorded thousands of cyclic tilt events within the crater. The duration of these events, from minutes to hours, was too long for them to be directly caused by the drumbeat seismicity. Tilt events were characterized by a recoverable, asymmetric pattern of rapid tilt away from the vent followed by a more gradual reversal, were highly correlated between different tiltmeters in the crater, sometimes occurred in association with volcanic seismicity, and ceased at the end of the eruption. Tilt vectors converged on a point just south of the center of the preexisting 1980s lava dome, and the absence of detectable tilt outside the crater suggests a shallow source (<1 km). We examine several models, including cycles of conduit pressurization and plug slip or gas loss and stick-slip behavior on the interface between the ascending plug and the 1980s lava dome. The small number of stations within the crater prevents a unique determination of source type or geometry, but results are consistent with a mechanism involving extrusion of the semisolid dacite plug and/or cycles of conduit pressurization.

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Section: The 2004-2008 Eruption Of Mount St Helensmentioning

confidence: 99%

Section: The 2004-2008 Eruption Of Mount St Helensmentioning

confidence: 99%

Section: Lf and Hybrid Earthquakesmentioning

confidence: 99%

Section: > > > > > > > > > > > > > > > 2 Earthquakesmentioning

confidence: 99%

Section: The 2004-2008 Eruption Of Mount St Helensmentioning

confidence: 99%

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Cyclic ground tilt associated with the 2004–2008 eruption of Mount St. Helens

2010

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Magma fracture and hybrid earthquakes in the conduit of Augustine Volcano

Buurman

West

2013

Geophysical Research Letters

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[1] We exploit subtle but systematic shifts in seismic waveforms to examine a 2 h cluster of repeating hybrid volcanic earthquakes preceding the first magmatic explosions at Augustine Volcano in January 2006. We extract differential P wave traveltimes of <0.01 s to determine that the source locations migrated downward by approximately 35 m. Waveform characteristics, GPS observations, and visual reports of lava effusion at the summit suggest that the earthquakes were sourced by fracturing magma in the upper conduit. As the lava cooled and degassed at the surface, the conditions in the upper conduit changed causing the zone in which magma fracture could occur to move downward through the magma column. These changes may also have been the first indicators that the conduit was becoming choked, causing a buildup in pressure that resulted in the large magmatic explosions that followed 36 h later. Citation: Buurman, H., and M. E. West (2013), Magma fracture and hybrid earthquakes in the conduit of Augustine Volcano, Geophys. Res. Lett., 40,[6038][6039][6040][6041][6042]

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Volcanic tremor masks its seismogenic source: Results from a study of noneruptive tremor recorded at Mount St. Helens, Washington

Denlinger

Moran

2014

JGR Solid Earth

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. This episode was remarkable both because no explosion followed, and because seismicity abruptly stopped following the episode. This sequence motivated us to consider a model for volcanic tremor that does not involve energetic gas release from magma but does involve movement of conduit magma through extension on its way toward the surface. We found that the tremor signal was composed entirely of Love and Rayleigh waves and that its spectral bandwidth increased and decreased with signal amplitude, with broader bandwidth signals containing both higher and lower frequencies. Our modeling results demonstrate that the forces giving rise to this tremor were largely normal to conduit walls, generating hybrid head waves along conduit walls that are coupled to internally reflected waves. Together these form a crucial part of conduit resonance, giving tremor wavefields that are largely a function of waveguide geometry and velocity. We find that the mechanism of tremor generation fundamentally masks the nature of the seismogenic source giving rise to resonance. Thus multiple models can be invoked to explain volcanic tremor, requiring that information from other sources (such as visual observations, geodesy, geology, and gas geochemistry) be used to constrain source models. With concurrent GPS and field data supporting rapid rise of magma, we infer that tremor resulted from drag of nearly solid magma along rough conduit walls as magma was forced toward the surface.

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Seismicity associated with renewed dome building at Mount St. Helens, 2004-2005

Cited by 71 publications

References 14 publications

Cyclic ground tilt associated with the 2004–2008 eruption of Mount St. Helens

Cyclic ground tilt associated with the 2004–2008 eruption of Mount St. Helens

Magma fracture and hybrid earthquakes in the conduit of Augustine Volcano

Volcanic tremor masks its seismogenic source: Results from a study of noneruptive tremor recorded at Mount St. Helens, Washington

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