Besides the main shock, the largest quake in this group measured magnitude 3.3. .
To verify the nonlinear site response at the site under main shock, the alternation of the site response was examined using the main shock and small event records before and after the main shock.
After the main shock, the earliest measurement was taken 32.0 h after the foreshock, that is, 4.0 h after the main shock.
After the main shock, the epicenters of aftershocks migrated from Kumamoto in NE and SW direction (Fig. 1).
If the fault plane of the largest aftershock is a part of the fault plane of the main shock, the Pacific plate must have moved northwestward during the main shock and southeastward during the largest aftershock.
Although the Choshi station (b) was rapidly uplifted immediately after the main shock, the vertical movement is predicted to gradually reverse to subsidence.
The large circles mark the epicenters of the M7.8 main shock, the M7.3 largest aftershock, and the M6.7 aftershock of April 26 , 2015
Seventeen days after the main shock, the largest aftershock of May 12, the M7.3 Kodari earthquake, occurred in the eastern extension of the primary aftershock zone.
The green star represents the epicenter of the main shock, the red circles represent large aftershocks (Mw >7.0), and the gray circles represent aftershocks (Mw >5.0).
