Fig. 2

Remote earthquake triggering during the passage of surface waves. a Continuous velocity waveforms observed at Hi-net and JMA stations (vertical components), showing remote triggering due to the Kumamoto earthquake. The waveforms are band-pass-filtered in the frequency range of 10–30 Hz and normalized to the maximum value on each seismogram. They are ordered function of epicentral distance, with distance increasing from up to down. Time is relative to the 01:25:00, on April 16, 2016 (i.e., 5 s before the occurrence time of the Kumamoto earthquake). The name of each recording station is indicated on the right of the plot. b Low-frequency vertical-component seismograms (0.01–0.2 Hz) observed at F-net stations located closely to the Hi-net stations in (a), ordered function of epicentral distance and normalized. The gray circles indicate P-wave arrival times of remotely triggered earthquakes, as observed at the Hi-net stations shown in (a). Gray inverted triangles in both a and b indicate the arrival of Rayleigh waves, for a phase velocity of 3.5 km/s