Fig. 4

b-value analysis for the period between the M6.9 and M6.8 earthquakes. a Map of b values obtained from the seismicity for the period from March 22, at 0:00 to May 1, at 10:26 (b_{2021/03/22–2021/05/01}), where we do not consider the period (March 20, at 18:10–March 21, 23:59) from immediately after the M6.9 March 20 earthquake to the end of March 21, avoiding the time period with large temporal variation in b. Other symbols are the same as in Fig. 1. b Δb (= b_{2021/03/22–2021/05/01} − b_{2018/01/01–2021/03/20}), subtraction of the b value in the bottom panel in Fig. 2a (b_{2018/01/01–2021/03/20}), from the b value in a (b_{2021/03/22–2021/05/01}). c logP_b, the logarithm of the probability that b_{2018/01/01–2021/03/20} and b_{2021/03/22–2021/05/01} are not different