Fig. 1

Detected aftershocks and their magnitudes. a Open circles and gray dots indicate the frequencies of identified aftershocks against magnitudes for the period between the main shock and the M7.3 largest aftershock, listed in the PDE catalog at May 13, 2015, and the ANSS catalog at October 31, 2015, respectively. The black and gray step functions are the cumulative numbers of identified aftershocks from the largest magnitude to the lowest, corresponding to the magnitude frequencies. b Magnitude versus elapsed time from the main shock on a logarithmic scale. Black and gray dots correspond to the identified aftershocks in the PDE catalog at May 13, 2015, and the ANSS catalog, respectively. The cumulative numbers of detected aftershocks plotted in red and in gray correspond to those from the PDE and ANSS catalogs, respectively. The black and blue horizontal lines represent the levels of M4.5 and M4.2, respectively. The red vertical dotted line indicates the start time of the target interval for fitting the aftershock models