Fig. 4

Stacked and envelope waveforms. Red traces in the upper panel show the waveform stacked from envelope waveform based on the travel time estimated from the optimal result for the source location of the triggered event. The time t = 0 on the horizontal axis is the origin time of the mainshock. Phases with large amplitudes before 30 s are the stacked phases of the mainshock. Black traces in the lower panels show envelope waveforms at strong-motion stations. The traces are sorted by epicentral distance based on the optimal result for the source location. Red squares indicate arrival times estimated from the optimal solution for the hypocenter of the triggered event