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Volcano earthquake sources associated with eruptions at Santiaguito volcano in Guatemala are complex. Rock fracture, fluid flow, and gas expansion occur at variable time scales and induce superposed ground motions, including both static and dynamic deformation, and atmospheric pressure disturbances. Dissection of this composite event is facilitated through extra‐seismic observations, such as infrasound, geodetic, and visual monitoring. Multi‐parametric investigation of an eruptive event on Jan. 4th 2009 reveals increased degassing, apparent as both geodetic tilt and harmonic seismo‐infrasonic tremor, preceding an explosive event. The explosive event itself entails surface dome uplift, multiple eruptive pulses, and subsequent re‐equilibration of the volcanic edifice manifested in derived tilt. We report here on an integrated approach to discerning the physical processes at the actively effusing and exploding Santiaguito volcano and describe the composite earthquake that occurs here.

Infrasound data are routinely used to detect and locate volcanic and other explosions, using both arrays and single sensor networks. However, at local distances (<15 km) topography often complicates acoustic propagation, resulting in inaccurate acoustic travel times leading to biased source locations when assuming straight-line propagation. Here we present a new method, termed Reverse Time Migration-Finite-Difference Time Domain (RTM-FDTD), that integrates numerical modeling into the standard RTM back-projection process. Travel time information is computed across the entire potential source grid via FDTD modeling to incorporate the effects of topography. The waveforms are then back-projected and stacked at each grid point, with the stack maximum corresponding to the likely source. We apply our method to three volcanoes with different network configurations, source-receiver distances, and topography. At Yasur Volcano, Vanuatu, RTM-FDTD locates explosions within ∼20 m of the source and differentiates between multiple vents. RTM-FDTD produces a more accurate location for the two Yasur subcraters than standard RTM and doubles the number of detected events. At Sakurajima Volcano, Japan, RTM-FDTD locates the source within 50 m of the active vent despite notable topographic blocking. The RTM-FDTD location is similar to that from the Time Reversal Mirror method, but is more computationally efficient. Lastly, at Shishaldin Volcano, Alaska, RTM and RTM-FDTD both produce realistic source locations (<50 m) for ground-coupled airwaves recorded on a four-station seismic network. We show that RTM is an effective method to detect and locate infrasonic sources across a variety of scenarios, and by integrating numerical modeling, RTM-FDTD produces more accurate source locations and increases the detection capability.

We present high‐broadband infrasound (0.01–100 Hz; 200‐Hz sample rate) observations of Vulcanian explosions at Popocatépetl volcano, Mexico. Popocatépetl is a highly active andesitic stratovolcano with regular violent explosions, making it a promising target for seismoacoustic observations. We deployed a four‐element broadband infrasound array (aperture 50 m) colocated with a compact broadband (120 s) seismometer at a site (ATLI) 15.8 km to the east‐southeast of Popocatépetl's summit. We highlight waveform examples from five powerful explosions during October to December 2017 that produced infrasound zero‐to‐peak pressure amplitudes ranging from 30 to 100 Pa at ATLI. The infrasound waveforms are highly asymmetric and are associated with clear air‐ground‐coupled arrivals on seismometers, with inverted vertical displacement waveforms tracking infrasonic pressure waveforms. Popocatépetl is close to major population centers, and array processing reveals persistent background infrasound from multiple directions, presumably of anthropogenic origin; our results have implications for infrasound monitoring at populated volcanoes.