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[S19-02] Estimation of the source of the explosive sound on April 26, 2021 in Hokkaido, Japan

〇Masumi YAMADA¹ (1.DPRI Kyoto University)

An explosive sound was heard over a wide area of Sapporo city, Hokkaido, Japan on April 26, 2021. It was accompanied by minor shaking and was considered likely to be a sonic boom produced by a fireball. However, no luminous phenomenon was observed. We analyzed seismic data to identify the source of the sonic boom, and estimated the trajectory of the object from the associated signal arrival times. The source was located approximately 100 km off the west coast of Hokkaido, at an altitude of 50 km. The elevation angle was higher than 66 degrees and the estimated velocity was higher than that of a fighter plane.
We compared trajectory models estimated from optical and seismic observations for past sonic boom events, and they were found to be in good agreement. Although our trajectory model is simplified and assumes that sound and the fireball have a constant speed, the model is highly accurate. The results show that seismic data can be used to estimate the trajectory of objects producing sonic booms, even when visual observations are unavailable.