The information of strength and stress of the crust is indispensable to understand the earthquake generation process. However, we have only insufficient knowledge about it and the crustal strength is still a subject of controversy. In order to settle the controversy, we A01 group members study the change in the focal mechanisms of small earthquakes before and after large earthquakes in detail. In order to obtain highly accurate focal solutions, we conduct dense seismograph observations in three areas with different stress situations: 1) from Akita to Fukushima prefectures where seismicity was activated after the 2011 M9.0 Tohoku-oki megathrust earthquake, 2) western Tottori prefecture where a M7.0 strike-slip fault type earthquake occurred in 2000, and 3) from southeastern Fukushima to northern Ibaraki prefectures where a M7.0 normal fault type earthquake occurred just after the 2011 Tohoku-oki earthquake. Based on the obtained information on spatiotemporal change in the focal mechanism solutions, we will estimate the distributions of strength and stress of the crust taking account of the results obtained by other groups.