Fig. 1

Acceleration waveforms for the Mw 7.0 Kumamoto earthquake of April 16, 2016, recorded at K-NET station OIT009 (Yufuin). a Raw waveforms. b Waveforms band-pass-filtered between 0.01 and 0.25 Hz by use of a one-pass operation. NS north–south motion, EW east–west motion, and UD vertical motion (up–down). The arrivals of P waves from the Kumamoto and triggered earthquakes are indicated by black arrows. The station location is shown in Figs. 2a and 3a