Temporal changes in stress preceding the 2004–2008 eruption of Mount St. Helens, Washington

Faulting within the Mount St. Helens conduit and implications for volcanic earthquakes

“…In contrast, the subsequent dome-forming phase of the eruption was instead accompanied by more than a million small (M d < 2.0) repetitive low-frequency "drumbeat" events, along with occasional larger earthquakes and very long period events (Lehto et al, 2010;Moran et al, 2008;Thelen et al, 2008;Waite et al, 2008). In addition, many more microearthquakes (as used here, earthquakes with M d < 0) occurred but were too small to be recorded except at near-vent seismic stations Thelen et al, 2008).…”

Influence of Stress Field Changes on Eruption Initiation and Dynamics: A Review

“…The first includes earthquakes and landslides (Stein, 1999;Hill et al, 2002;Harris and Ripepe, 2007;Walter, 2007;Watt et al, 2008;De la Cruz-Reyna et al, 2010), while the second comprises unloading due to erosion and deglaciation (Davydov et al, 2005;Sigmundsson et al, 2010), tidal effects (Sohn, 2004;Cazaneve and Chen, 2010), or changes in the tectonic regime (Ventura and Vilardo, 1999;Waite and Smith, 2004;Diez et al, 2005;Miura and Wada, 2007;Lehto et al, 2010;Carbone et al, 2014). These processes superimpose to the possible local stress variations related to internal dynamics of a volcano, such as pressure increase in the magma chamber due to magma influx from depth or buoyancy induced by magma differentiation processes (Massol and Jaupart, 1999;Gudmundsson, 2006Gudmundsson, , 2016Cañon-Tapia, 2014).…”

Interaction between regional and magma-induced stresses and their impact on volcano-tectonic seismicity

“…In this case, most of the VTs are located in a rather limited depth range and most of the VT events had pure or oblique strike-slip mechanisms (Roman et al, , 2008. Other similar examples showing variability in the focal mechanisms during periods preceding or accompanying significant eruptive activity have been noted at Guagua Pichincha, Ecuador (Legrand et al, 2002), Mount Unzen, Japan (Umakoshi et al, 2001), Popocatépetl, Mexico (Arámbula-Mendoza et al, 2010 and Mount St. Helens, Washington (Lehto et al, 2010). Uprising and intruding magma has been hypothesized as the cause of these major changes in the direction of the pressure axes.…”