High‐Broadband Seismoacoustic Signature of Vulcanian Explosions at Popocatépetl Volcano, Mexico.

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. Plain Language Summary: Seismology and acoustics are complementary methods for quantifying volcanic eruption processes, corresponding to elastic wavefields propagating through the solid Earth and acoustic wavefields propagating through the fluid atmosphere, respectively. Seismic data currently form the backbone of most volcano‐monitoring systems. Seismic signals at erupting volcanoes capture subsurface magma transport and rapid depressurization associated with explosive eruptions. Infrasound (acoustic waves with frequencies below 20 Hz, the lower‐frequency limit of human hearing) is a newer technology; infrasound data record subaerial degassing and allow physical quantification of explosive eruption mechanisms. Popocatépetl is one of the two most active volcanoes in Mexico (together with Volcán de Colima) and a prodigious source of explosive activity, making it an obvious target for combined seismic and infrasound (seismoacoustic) observations. We recorded continuous infrasound and seismic waveform data at a site 15.8 km to the east‐southeast of Popocatépetl for several months, capturing five powerful explosions. Our data were collected at a location where local people report hearing sounds associated with visual observations of explosions from Popocatépetl. Part of the motivation of this work is to investigate the capability of infrasound stations at distances greater than 5 km to monitor Popocatépetl with significantly reduced risk exposure to field personnel and instrumentation. Key Points: Infrasound array study of Popocatépetl; high broadband (200‐Hz sample rate) includes sub‐bass rangeVulcanian explosions produce high‐amplitude asymmetric infrasound, which is air‐ground coupledInverted vertical displacement seismic waveforms track infrasonic pressure waveforms [ABSTRACT FROM AUTHOR]