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We present high-broadband infrasound (0.01-100 Hz; 200-Hz sample rate) observations of Vulcanian explosions at Popocatepetl volcano, Mexico. Popocatepetl 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 50m) colocated with a compact broadband (120s) seismometer at a site (ATLI) 15.8km to the east-southeast of Popocatepetl'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 100Pa 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. Popocatepetl 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 20Hz, the lower-frequency limit of human hearing) is a newer technology; infrasound data record subaerial degassing and allow physical quantification of explosive eruption mechanisms. Popocatepetl is one of the two most active volcanoes in Mexico (together with Volcan 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 15.8km to the east-southeast of Popocatepetl 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 Popocatepetl. Part of the motivation of this work is to investigate the capability of infrasound stations at distances greater than 5km to monitor Popocatepetl with significantly reduced risk exposure to field personnel and instrumentation.