Seismic Envelope‐Based Detection and Location of Ground‐Coupled Airwaves from Volcanoes in Alaska

Abstract

Volcanic explosions and other infrasonic sources frequently produce acoustic waves that are recorded by seismometers. Here we explore multiple techniques to detect, locate, and characterize ground-coupled airwaves (GCA) on volcano seismic networks in Alaska. GCA waveforms are typically incoherent between stations, thus we use envelope-based techniques in our analyses. For distant sources and planar waves, we use f-k beamforming to estimate back azimuth and trace velocity parameters. For spherical waves originating within the network, we use two related time difference of arrival (TDOA) methods to detect and localize the source. We investigate a modified envelope function to enhance the signal-to-noise ratio and emphasize both high energies and energy contrasts within a spectrogram. We apply these methods to recent eruptions from Cleveland, Veniaminof, and Pavlof Volcanoes, Alaska. Array processing of GCA from Cleveland Volcano on 4 May 2013 produces robust detection and wave characterization. Our modified envelopes substantially improve the shortterm average/long-term average ratios, enhancing explosion detection. We detect GCA within both the Veniaminof and Pavlof networks from the 2007 and 2013-2014 activity, indicating repeated volcanic explosions. Event clustering and forward modeling suggests that high-resolution localization is possible for GCA on typical volcano seismic networks. These results indicate that GCA can be used to help detect, locate, characterize, and monitor volcanic eruptions, particularly in difficult-to-monitor regions. We have implemented these GCA detection algorithms into our operational volcanomonitoring algorithms at the Alaska Volcano Observatory.

Local, Regional, and Remote Seismo‐acoustic Observations of the April 2015 VEI 4 Eruption of Calbuco Volcano, Chile

“…The seismo‐acoustic cross‐correlation and coherence analysis and observed polarization change above 2 Hz for the seismic data indicate that air‐ground coupling is a significant component of the seismic eruption tremor waveforms at regional distances (Figures and ). Thus, existing seismic networks can help improve the infrasonic network detection capability (e.g., Cochran & Shearer, ; Fee et al, ; Hedlin et al, ).…”

Remote Detection and Location of Explosive Volcanism in Alaska With the EarthScope Transportable Array

“…The majority of volcanoes of interest in Alaska are outside the margins of the bulk of monitoring stations, and consequently incorporation of an independent location estimate provided by local infrasound arrays would provide this azimuthal control. These arrays can provide individual back azimuths (Fee et al, ; Fee, Steffke, & Garcés, ; Gibbons et al, ; Iezzi et al, ; Le Pichon et al, ; Ripepe et al, ), and distances (Green & Nippress, ; Shang et al, ; Shani‐Kadmiel, Assink, Smets, et al, ; Szuberla et al, ), in addition to source triangulation through a cross‐bearings approach (e.g., Le Pichon et al, ; Matoza, Le Pichon , et al, ; Matoza, Vergoz, et al, ; Mialle et al, ; Matoza et al, ). The relative consistency with which stacked array data characterizes eruption records, when compared to a network of single sensors demonstrates the importance of these arrays.…”

“…Global infrasound networks have been shown to be effective at detecting relatively violent eruptions, even in remote locations (Dabrowa et al, ; Evers & Haak, ; Fee, Steffke, & Garcés, ; Fee et al, ; Le Pichon et al, ; Liszka & Garcés, ; Matoza et al, ; Matoza et al, ; Matoza, Le Pichon , et al, ; Matoza, Vergoz, et al, ). Local infrasound networks (sources <15 km distant), however, are better placed for identifying smaller explosions, degassing, or effusive behavior within a limited radius (e.g., De Angelis et al, ; Fee et al, ; Fee, Garcés, et al, ; Johnson et al, ; Jolly et al, ; Matoza et al, ; Petersen & McNutt, ). A dense regional seismoacoustic network such as the TA falls between these two endmember network geometries, affording an unprecedented opportunity to evaluate explosive volcanic eruptions, wave propagation, coupling, and signal evolution for source‐sensor ranges out to a few thousand kilometers (e.g., study of the Pavlof March 2016 eruption by Fee et al, ).…”

Infrasound Signal Detection and Back Azimuth Estimation Using Ground‐Coupled Airwaves on a Seismo‐Acoustic Sensor Pair

“…• Data Set S18 • Data Set S19 to the ground as a seismic wave, known as a ground-coupled airwave (GCA). GCAs from a variety of sources including volcanoes, bolides, meteors, and explosions are regularly detected on seismometers (De Angelis et al, 2012;Edwards et al, 2007;Fee et al, 2016Fee et al, , 2017Ichihara et al, 2012;Johnson & Malone, 2007;Langston, 2004;Matoza & Fee, 2014;Nishida & Ichihara, 2015;Smith et al, 2016;Tauzin et al, 2013;Walker et al, 2010). Here we present a method to determine the back azimuth to an acoustic source detected on a nearly collocated three-component seismometer and infrasonic microphone.…”

“…A frequently observed phenomenon in infrasonic wave propagation is when an incident acoustic wave traveling through the atmosphere encounters the Earth's surface and part of the wave energy is transferred to the ground as a seismic wave, known as a ground‐coupled airwave (GCA). GCAs from a variety of sources including volcanoes, bolides, meteors, and explosions are regularly detected on seismometers (De Angelis et al, ; Edwards et al, ; Fee et al, , ; Ichihara et al, ; Johnson & Malone, ; Langston, ; Matoza & Fee, ; Nishida & Ichihara, ; Smith et al, ; Tauzin et al, ; Walker et al, ). Here we present a method to determine the back azimuth to an acoustic source detected on a nearly collocated three‐component seismometer and infrasonic microphone.…”