Abstract The size distribution of minor earthquakes, characterized by a power-law decay (b-value), sometimes indicates the hazard information of major earthquakes. Studies show that the b-value reflects the stress level and proximity of the fault failure condition. However, the mechanisms are difficult to determine. This study proposes an additional proximity indicator that is ratio of stacked seismic moment tensor to total moment release in a volume. The ratio indicates efficiency of inelastic strain due to seismic moment release by earthquakes, being close to the strength of the medium based on the Mohr diagram and Coulomb failure condition. We examined the b-value and efficiency variations in pre- and post-seismic activities of the 2016 Kumamoto earthquake sequence. The weighted b-value distribution based on efficiency captured the initiation point of the Kumamoto earthquake. Thus, utilizing both b-value and efficiency can improve earthquake alerts and disaster mitigation.