Fig. 1

Schematic illustration of the method. a Flowchart of selection of earthquake catalog. b Procedure for removal of aftershocks of a large earthquake (Step 1). \({D}_{\mathrm{min}}\) represents the extent of the aftershock area and \({t}_{d}\) represents the duration of the aftershock sequence. c Procedure for selection of source and dependent events (Step 2). We select the first earthquake \({q}_{1}\) as a source event (\({E}_{0}^{1})\) and search for its dependent events \({q}_{3}\). We do not use \({q}_{2}\) as a dependent event, because it occurs within a horizontal distance of \({D}_{\mathrm{min}}\) from the source event (i.e., it is treated as an aftershock of the source event). The event \({q}_{4}\) is selected as a source event (\({E}_{0}^{2})\) and \({q}_{5}\) is selected as a dependent event. The event \({q}_{6}\) is a source event (\({E}_{0}^{3})\) and \({q}_{7}\) is its dependent event. The event \({q}_{8}\) is selected as a source event (\({E}_{0}^{4})\) with a dependent event \({q}_{12}\), but \({q}_{9}\) is not a dependent event. The event \({q}_{10}\) is a source event (\({E}_{0}^{5})\) with two dependent events \({q}_{11}\) and \({q}_{13}\)