An Analysis of Dense Seismoacoustic Signals from an Accidental Chemical Explosion in South Korea on 4 March 2020

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Abstract
On 4 March 2020, an accidental explosion occurred at a chemical plant in South Korea, generating both seismic and infrasound signals, which were recorded by multiple sensors at distances as great as 400 km across the southern Korean Peninsula. We used seismic and infrasound data recorded at 5 seismoacoustic arrays, 4 infrasound arrays, 13 single infrasound stations, the KSRS array, and single seismometers from several networks to quantify the explosion characteristics. Seismic, infrasound, and air-to-ground coupled acoustic arrivals from the explosion and coda-like signals from secondary sources are identified based on array processing and analyst review. We estimated the explosion origin time and location using combined seismic Lg and infrasound backprojection methods, demonstrating the importance of the dense network data using both wavefield types. We also found that dense network data can reduce the uncertainty in the location estimation using P arrivals and infrasound back azimuths. Yield estimates using infrasound amplitudes provide a 95% confidence from 1.3 to 3.2 tons with a maximum a posteriori of 1.9 tons, determined using propagation-based, stochastic path geometry models. The methods in this study document a seismoacoustic examination procedure that can be used in forensic investigations to detect, locate, and characterize anthropogenic sources.

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