Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers

Abstract

[1] Multiplets, or groups of earthquakes with similar waveforms, are commonly observed at volcanoes, particularly those exhibiting unrest. Using triggered seismic data from the 1980-1986 Mount St. Helens (MSH) eruption, we have constructed a catalog of multiplet occurrence. Our analysis reveals that the occurrence of multiplets is related, at least in part, to the viscosity of the magma. We also constructed catalogs of multiplet occurrence using continuous seismic data from the 2004 eruption at MSH and 2007 eruption at Bezymianny Volcano, Russia. Prior to explosions at MSH in 2004 and Bezymianny in 2007, the multiplet proportion of total seismicity (MPTS) declined, while the average amplitudes and standard deviations of the average amplitude increased. The life spans of multiplets (time between the first and last event) were also shorter prior to explosions than during passive lava extrusion. Dome-forming eruptions that include a partially solidified plug, like MSH (1983MSH ( -1986MSH ( and 2004MSH ( -2008, often possess multiplets with longer life spans and MPTS values exceeding 50%. Conceptually, the relatively unstable environment prior to explosions is characterized by large and variable stress gradients brought about by rapidly changing overpressures within the conduit. We infer that such complex stress fields affect the number of concurrent families, MPTS, average amplitude, and standard deviation of the amplitude of the multiplets. We also argue that multiplet detection may be an important new monitoring tool for determining the timing of explosions and in forecasting the type of eruption.Citation: Thelen, W., S. Malone, and M. West (2011), Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers,

Renewed Explosive Phreatomagmatic Activity at Poás Volcano, Costa Rica in April 2017

“…The further classification of seismic events into "families, " which all have a similar waveform shape as well as the same frequency content, allows the depiction of temporal and spatial changes in the source mechanism and the source location on a much smaller scale (e.g., Thelen et al, 2011;Salvage and Neuberg, 2016). By definition, families of seismic events should be generated by the same source mechanism and at the same source location (estimated at between one quarter and one tenth of the wavelength; Geller and Mueller, 1980;Neuberg et al, 2006) in order for the detected waveforms to have the same recorded shape at the seismometer (Minakami et al, 1951), as long as site and path effects on the seismic wave are minimal.…”

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

“…Repeating LF waveforms have been observed in many different types of volcanic settings, including dome-forming eruptions at Redoubt, Alaska; Unzen, Japan; Mount St Helens, Washington; Bezymianny, Kamchatka; and SHV Lamb et al, 2015;Thelen et al, 2011;West, 2013;Green and Neuberg, 2006;Ottemöller, 2008;De Angelis, 2009]; at persistently restless volcanoes such as Telica, Nicaragua, and Shishaldin, Alaska [Rodgers et al, 2013[Rodgers et al, , 2015aPetersen, 2007]; and at basaltic systems such as Kilauea, Hawaii [Battaglia et al, 2003]. Repeating families (multiplets) are often used to improve locations [Battaglia et al, 2003], determine depth of explosive activity [West, 2013;Thelen et al, 2011], constrain source mechanisms , and assess the stability of seismic sources [Rodgers et al, 2013] and the stability of stress fields [West, 2013]. Figure 1) began erupting in 1995, and for the last 20 years has repeatedly transitioned between quiescent, effusive, and explosive phases of activity ( Figure 2) [Kokelaar, 2002;Wadge et al, 2014].…”

“…Repeating earthquakes are found during most significant seismic swarms at volcanoes [ West , ], and their presence alone is not indicative of eruptive processes. Repeating LF waveforms have been observed in many different types of volcanic settings, including dome‐forming eruptions at Redoubt, Alaska; Unzen, Japan; Mount St Helens, Washington; Bezymianny, Kamchatka; and SHV [ Power et al , ; Lamb et al , ; Thelen et al , ; West , ; Green and Neuberg , ; Ottemöller , ; De Angelis , ]; at persistently restless volcanoes such as Telica, Nicaragua, and Shishaldin, Alaska [ Rodgers et al , , ; Petersen , ]; and at basaltic systems such as Kilauea, Hawaii [ Battaglia et al , ]. Repeating families (multiplets) are often used to improve locations [ Battaglia et al , ], determine depth of explosive activity [ West , ; Thelen et al , ], constrain source mechanisms [ Green and Neuberg , ], and assess the stability of seismic sources [ Rodgers et al , ] and the stability of stress fields [ West , ].…”

Volcano Seismology: Detecting Unrest in Wiggly Lines

“…The choice of similarity threshold is important: if it is too low there is a risk of placing events which are not similar into the same family; if it is too high similar events can be missed. Green and Neuberg (2006), Thelen et al (2011) and Salvage and Neuberg (2016) suggest a cross correlation coefficient threshold of 0.7, since this is significantly above the correlation coefficient that can be produced from random correlations between noise and a waveform. Higher cross correlation coefficient thresholds can be used to identify families of almost identical waveforms, however Petersen (2007) suggests that this is probably not appropriate in volcanic settings due to additional noise in this environment.…”

“…The further classification of seismic events into families which all have a similar waveform shape, as well as the same frequency content, allows the depiction of temporal and spatial changes in the source mechanism and the source location on a much smaller scale (e.g. Thelen et al 2011;Salvage and Neuberg 2016). For example, the relative relocation of families of similar seismic events at Soufrière Hills volcano, Montserrat has produced very precise source locations (e.g.…”