Electronic Supplement to
Acoustic Characterization of Explosion Complexity at Sakurajima, Karymsky, and Tungurahua Volcanoes

by Robin S. Matoza, David Fee, and Taryn M. López

Propagation Effects at Sakurajima

The extracted signal metrics can be readily used to evaluate infrasound propagation effects for the Sakurajima network. This also provides a validation that the recovered peak pressure and energy estimates make physical sense. Figure S1 shows the event onset peak pressure (ppeak) and energy (Eonset) across the Sakurajima network, with values normalized to those at station ARI (2.3 km from the active vent in Showa crater). Median values at each station are offset from those predicted by theoretical free-field geometrical spreading (no topography). The relative offsets are broadly consistent with the topographic profiles to each station (see Fee et al., 2014) and indicate topographic effects (Matoza et al., 2009b; Kim and Lees, 2011, 2014; Lacanna and Ripepe, 2013; Lacanna et al., 2014). The spread at each station may be explained by a combination of measurement error in the automatic method, time-varying propagation effects due to wind and temperature (e.g. Fee and Garcés, 2007; Matoza et al., 2009), nonmonopole anisotropic source effects (e.g., Johnson et al., 2008; Kim et al., 2012), and frequency-dependent diffraction effects (variable event frequency content may lead to variable diffraction effects; Lacanna and Ripepe, 2013). Infrasound propagation across the network is discussed and modeled further in the paper by Kim and Lees (2014). Limiting the analysis to higher-amplitude events (ppeak≥10 Pa at station ARI) dramatically reduces the scatter in ppeak / ppeakARI and Eonset/EonsetARI (Figures S1c, d). An explanation for this is that errors in estimated ppeak or Eonset at a given station are a greater proportion of the absolute value ppeakARI or EonsetARI for smaller events. A similar analysis of the propagation effects is not possible for the Tungurahua or Karymsky data sets, as the maximum interelement separations of ~100 m cannot resolve the larger-scale propagation effects.


Figure

Figure S1. Event onset (a) peak pressure (ppeak) and (b) energy (Eonset) across the Sakurajima network for all 74 explosions, with values normalized to station ARI (2.3 km from the active Showa crater). The dashed lines indicate theoretical geometrical spreading of (a) 1/r and (b) 1/r2. The data at each station are represented as boxplots with dark gray lines at the medians, gray boxes indicating the interquartile range, and black whiskers representing the full data range. Static offsets of the median values from the geometrical spreading laws indicate time-invariant topographic effects (e.g., Lacanna and Ripepe, 2013), while the spread indicates time-varying propagation effects and measurement error in the automatic picks. (c) and (d) are the same as (a) and (b), but show only the 34 events with ppeak≥10 Pa at station ARI.


References

Fee, D., and M. Garcés (2007). Infrasonic tremor in the diffraction zone, Geophys. Res. Lett. 34, no. 16.

Fee, D., A. Yokoo, and J. B. Johnson (2014). Introduction to an open community infrasound dataset from the actively erupting Sakurajima Volcano, Seismol. Res. Lett.,85, no. 6, doi: 10.1785/0220140051.

Johnson, J., R. Aster, K. R. Jones, P. Kyle, and B. McIntosh (2008). Acoustic source characterization of impulsive Strombolian eruptions from the Mount Erebus lava lake, J. Volcanol. Geoth. Res. 177, no. 3, 673–686.

Kim, K., and J. M. Lees (2011). Finite-difference time-domain modeling of transient infrasonic wavefields excited by volcanic explosions, Geophys. Res. Lett. 38, no. 6).

Kim, K., and J. Lees (2014), Volcano infrasound propagation at Sakurajima, Japan, with GPU-accelerated 3D modeling, Seismol. Res. Lett. 85, no. 6, doi: 10.1785/0220140058.

Kim, K., J. M. Lees, and M. Ruiz (2012). Acoustic multipole source model for volcanic explosions and inversion for source parameters, Geophys. J. Int. 191, no. 3, 1192–1204.

Lacanna, G., and M. Ripepe (2013). Influence of near-source volcano topography on the acoustic wavefield and implication for source modeling, J. Volcanol. Geoth. Res. 250, 9–18.

Lacanna, G., M. Ichihara, M. Iwakuni, M. Takeo, M. Iguchi, and M. Ripepe (2014). Influence of atmospheric structure and topography on infrasonic wave propagation, J. Geophys. Res. 119, no. 4, 2988–3005.

Matoza, R. S., M. A. Garcés, B. A. Chouet, L. D’Auria, M. A. Hedlin, D. Groot-Hedlin, and G. P. Waite. (2009). The source of infrasound associated with long-period events at Mount St. Helens. J. Geophys. Res. (1978–2012) 114, no. B4.

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