Yield estimation and event discrimination of the 4 August 2020 Beirut chemical explosion

We investigate the 4 August 2020 Beirut accidental chemical explosion based on regional seismic data recorded at both on- and off-shore stations. The Lg-wave body-wave magnitude is mb(Lg)=3.30+ or -0.46 for the Beirut explosion. The explosive yield obtained using an empirical magnitude-yield relation based on a fully buried explosion source model is only 0.112 kt. Alternatively, the yield estimated using an empirical relation between the yield and crater size is 1.22 kt, with the uncertainties between 0.48 and 2.3 kt. The latter is closer to reality. The P/S spectral amplitude ratios, including Pg/Lg, Pn/Lg, and Pn/Sn, are calculated for the Beirut explosion and nearby natural earthquakes. We find the P/S spectral ratios are effective in discriminating the explosion from earthquakes in the Northwestern Arabia plate. By comparing the spectral ratios of large open-pit explosions, including the Beirut, Xiangshui, and Tianjin explosions, with those from historical nuclear explosions, buried small chemical explosions, and natural earthquakes, we further investigate the detailed differences of network-averaged P/S spectral ratios between different source types.