Fig. 2

Seismic and EM recordings of an aftershock. This is a M5.4 aftershock occurring at 01:44 (in JST) on April 16, 2016, that is, 19 min after the mainshock of M7.3 Kumamoto earthquake. The recordings are displayed in a Cartesian and b cylindrical coordinates, respectively. The seismic and EM time series in this figure are displayed at 32 Hz sampling rate. Thus, the frequency band of the recordings is 0–16 Hz