Fig. 3

b-value maps for different sampling radii: a\( r = 20\,\,{\text{km}} \); b\( r = 30\,{\text{km}} \); c\( r = 35\,{\text{km}} \); d\( r = 40\,{\text{km}} \); e\( r = 50\,{\text{km}} \). c Data were used in the subsequent analysis. If fewer than 50 events were located within the search radius of a grid node, the corresponding b-value was not mapped