The Japan region is characterized by intense seismic activity. This catalog consists of earthquakes in a polygon bounded by 129°27'-144°73' E and 26°96'-43°04' N and from March 6, 2003, to July 10, 2023, obtained from the Japanese Meteorological Agency [1,2]. Aftershocks were identified using Molchan–Dmitrieva’s algorithm [3], which relies on the statistical analysis of the spatiotemporal distribution of seismic events. The aftershocks were subsequently marked using the program described in [4], which is an adaptation of the earlier program developed by Smirnov [5].