- © 2014 by the Seismological Society of America
A variety of techniques have been employed to locate seismic and acoustic signals at volcanoes. A common source location method in volcano acoustics at local distances (e.g., <10 km) is semblance, a forward grid‐search technique modified for volcano seismic signals by Kawakatsu et al. (2000) and Almendros and Chouet (2003). Other techniques for source location include Bayesian infrasonic source location (Modrak et al., 2010) and time‐reversal acoustics (Kim and Lees, 2014). The semblance coefficient, on which this method is based, was first introduced by Neidell and Taner (1971) and defined as a time‐domain measure of the coherency (i.e., the similarity) of multichannel data. This method is attractive for volcano acoustic source localization, as it does not rely on a detailed velocity model, which is generally not available around volcanoes. The computation is also straightforward, and the resulting semblance maps provide an intuitive visualization of the source location. Semblance has been applied in 2D and 3D at a number of volcanoes, including Stromboli (Ripepe and Marchetti, 2002; Ripepe et al., 2009), Etna (Montalto et al., 2010; Cannata et al., 2011), Erebus (Jones et al., 2008), Santiaguito (Johnson et al., 2011; Jones and Johnson, 2011), and Karymsky (Rowell et al., 2014). Rowell et al. (2014) also used a time‐difference‐of‐arrival localization method at Karymsky Volcano, with mixed results. At greater distances (e.g., >10 km), localization from back‐azimuth cross‐bearings from multiple arrays has been an effective technique (Matoza et al., 2011; Johnson et al., 2013) but typically requires accounting for wind and atmospheric structure. In addition to source localization, semblance has also been shown effective at identifying a variety of eruption phenomena (i.e., explosive eruptions, degassing events, and rockfalls) (Johnson et al., 2011). All of the aforementioned methods are often limited by a relatively small number of stations and poor vertical resolution.