令和元年東日本台風通過時に福島県東部で観測された脈動について

抄録

Large amplitude microseisms were recorded during the passage of typhoon Hagibis in 2019 at the Hirono Thermal Power Station (HRN) located in the middle of eastern Fukushima Prefecture. The amplitude of microseisms during the passage of typhoon Hagibis was 10 to 20 times the amplitude of microseisms when there was no typhoon. The dominant period of microseisms was about 5 seconds just before the typhoon passage and about 6 seconds after the typhoon passage. The amplitude of microseisms at HRN is much larger (10 times more) than those at F-net Hirono (HRO) station on bedrock, but the predominant period is almost the same except for the vertical component after the typhoon passage. The same predominant period cannot be considered from each underground structure model. The predominant period is determined by the source of microseisms. Coherence analysis using three components of HRO station’s record suggests that the Rayleigh wave is the main component of observed microseisms. On the other hand, the same tendency was not derived from the coherence of HRN, possibly due to the superposition of other wave components. The temporal change of amplitude of microseisms shows a different pattern from those of the significant wave height recorded off the coast of Fukushima, and the predominant period of microseisms did not correspond to 1/2 of the significant wave period. The source of microseisms after the passage of a typhoon needs to be considered not only in the sea area near the coast but also in the offshore sea area.