Assessing the likelihood and magnitude of volcanic explosions based on seismic quiescence

Abstract

Available online xxxx Editor: P. Shearer Keywords: volcano monitoring volcanic hazards phreatic explosions seismic quiescence Telica VolcanoVolcanic eruptions are generally forecast based on strong increases in monitoring parameters such as seismicity or gas emissions above a relatively low background level (e.g., Voight, 1988;Sparks, 2003). Because of this, forecasting individual explosions during an ongoing eruption, or at persistently restless volcanoes, is difficult as seismicity, gas emissions, and other indicators of unrest are already in a heightened state. Therefore, identification of short-term precursors to individual explosions at volcanoes already in heightened states of unrest, and an understanding of explosion trigger mechanisms, is important for the reduction of volcanic risk worldwide. Seismic and visual observations at Telica Volcano, Nicaragua, demonstrate that a) episodes of seismic quiescence reliably preceded explosions during an eruption in May 2011 and b) the duration of precursory quiescence and the energy released in the ensuing explosion were strongly correlated. Precursory seismic quiescence is interpreted as the result of sealing of shallow gas pathways, leading to pressure accumulation and eventual catastrophic failure of the system, culminating in an explosion. Longer periods of sealing and pressurization lead to greater energy release in the ensuing explosion. Near-real-time observations of seismic quiescence at restless or erupting volcanoes can thus be useful for both timely eruption warnings and for forecasting the energy of impending explosions.

Origin of Shallow Volcanic Tremor: The Dynamics of Gas Pockets Trapped Beneath Thin Permeable Media

“…In contrast, our model predicts that transitions from monochromatic to broadband tremor, systematic decreases of seismic amplitude, and slight frequency gliding (upward or downward) may be indicative of sealing. Cap sealing may therefore explain the seismic quiescence (i.e., low seismic amplitude) detected prior to gas explosions at Telica (Roman et al, ) and Fuego (Nadeau et al, ); and the emergence of a clear broadband signal at Kawah Ijen volcano at least 14 hours prior to a phreatic eruption on 20 March 2013 (Figure ). Our model also predicts that subtle downward frequency gliding may reflect increase of the molecular weight of the gas supplied (e.g., associated with the ascent of deep CO 2 (Burton et al, )).…”

Quiescent‐explosive transitions during dome‐forming volcanic eruptions: Using seismicity to probe the volcanic processes leading to the 29 July 2008 vulcanian explosion of Soufrière Hills Volcano, Montserrat

“…The low rates of seismicity before the eruption may appear inconsistent with a model of increasing pressurization that would predict increasing rates of VT seismicity until failure [ Voight , ]. However, low rates of seismicity during precursory pressurization have been observed at other systems [ Fischer et al , ; Nishimura et al , ; Roman et al , ], and although these studies focus primarily on LF events, we note the similar lack of VT seismicity before these eruptions. The low rate of VT seismicity we observed before the July 2008 explosion at SHV (Figure d) may be due to the Kaiser effect, whereby rock fracturing does not occur until stress levels have reached a previously attained level [ Kaiser , ; Lavrov , ].…”

“…Alternatively, sealing of the magma outgassing process may reduce pore fluid pressure in the surrounding VT source area, and while pressure may increase inside the magmatic system, the lack of pore fluid pressure may inhibit rock fracture in the surrounding seismogenic zone [ Byerlee , ]. Thus, our observation of precursory quiescence during a period of final pressurization is consistent with previous models of this explosion [ Gottsmann et al , ] and with models of preeruptive seismic quiescence at other volcanoes globally [ Fischer et al , ; Nishimura et al , ; Roman et al , ].…”

“…Precursory quiescence has been observed before vulcanian eruptions in a variety of settings [Hotovec et al, 2013;Nishimura et al, 2013;Roman et al, 2016] and has been attributed to mechanisms such as sealing of a shallow magmatic-hydrothermal system [Rodgers et al, 2013;Nishimura et al, 2013;Geirsson et al, 2014;Rodgers et al, 2015b] or crystallization in a magma conduit preventing magma outgassing [Fischer Journal of Geophysical Research: Solid Earth 10.1002/2016JB013180 et al, 1994. In this instance, the large vulcanian explosion occurred at 03:32 UTC on 29 July, after~7 h of relative seismic quiescence, especially in terms of VT earthquakes (Figure 3).…”

Driving magma to the surface: The 2011–2012 El Hierro Volcanic Eruption

“…During the final stages of preeruptive volcanic unrest, certain geophysical and geodetical features are usually observed: an overall acceleration in seismicity and ground deformation [e.g., Bell and Kilburn , ], shallower seismicity [e.g., Battaglia et al ., ], seismic migration [e.g., Caudron et al ., ], and an apparent lack of activity (hours to minutes) before the reinforcement or the onset of the eruption [e.g., Roman and Heron , ]. Several well‐documented eruptions show some, if not all, of these precursory features [e.g., Vinciguerra , ; Battaglia et al ., ; Bell and Kilburn , ; López et al ., ; Sigmundsson et al ., ; Caudron et al ., ], which suggests that similar fundamental processes may occur within these volcanoes.…”