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Volcanic Eruption Infrasound
ity. Yasur volcano was chosen for this experiment because it is highly active and offered the chance to test the novel aerostat-based acquisition system. The coincident ground- based seismo-acoustic deployment lasted only about 8 days but recorded more than 8,000 infrasound explosion signals and more than 10,000 volcanic earthquakes. Infrasound sig- nals exceeded 500 Pa at 300 m from the vent.
Current State of Volcano
Infrasound Monitoring
At present, numerous volcano observatories are using infra- sound to detect, locate, and characterize volcanic eruptions. The recent eruption of Bogoslof volcano, Alaska (Figure 2), produced over 60 powerful explosions in a span of 8 months (see No local monitoring was possible due to the hazard and small size of this remote island, yet each eruption produced volcanic emissions that posed a danger to aircraft, passing ships, and a nearby fishing port. In conjunc- tion with seismic, satellite, and lightning data, AVO used data from multiple infrasound arrays in the region, at distances from 60 to 820 km, to detect and characterize eruptions in near-real-time. Automated array-processing algorithms en- abled detection of both short-duration explosions and lon- ger duration jetting, with relevant AVO personnel receiving eruption alerts via text message and email. Infrasound was particularly useful in this scenario due to the remoteness of Boglosof and the complex nature of this eruption.
Figure 2, c and d, shows the waveforms and spectrogram of a Bogoslof eruption on January 31, 2017, as detected on an infrasound array (named OKIF) on Umnak Island 60 km away. The eruption begins with a number of short-duration, impulsive explosions and then transitions to multiple jet- ting phases. AVO observed these various eruptive phases in near-real-time and inferred a change in eruption style from subaqueous to subaerial that was later found to be consistent with other observations. The source depth is a key compo- nent used in estimating the volcanic emissions hazard.
Major progress has been made in using infrasound to under- stand and monitor volcanic eruptions, and the technology has matured into an essential tool for many volcano scientists. However, numerous questions remain. Quantitative source models are only available for a limited range of volcanic pro- cesses. Further developed quantitative models of the infra- sonic source have the potential to improve estimates of criti- cal eruption characteristics such as the amount, location, and type of volcanic emissions. Infrasound propagation modeling also continues to improve through refinements in atmospher-
24 | Acoustics Today | Spring 2018
ic specifications and numerical models and through increases in computational capacity. For example, wind is often ne- glected in full-waveform infrasonic modeling but can signifi- cantly affect the wave propagation. Dense networks of high- quality infrasound sensors deployed at various distances and azimuths from the volcanic vent will provide valuable data to test source and propagation models. Continued development of algorithms for local and remote automated detection, asso- ciation, and location of volcanic eruption infrasound signals will improve hazard monitoring.
This work was supported by National Science Foundation Grants EAR-1614855, EAR-1620576, EAR–1614323, and EAR-1331084. We thank Editor Arthur Popper for helpful comments.
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