  Crustal deformation due to the 2016 earthquake sequence in Kumamoto, Japan,
that culminated in a preceding earthquake of magnitude M6.5 and a subsequent
M7.3 earthquake 28 hours later, caused stress perturbation on and around the
causative Futagawa-Hinagu fault zone. Monitoring changes in seismicity pattern
along this zone plays a role in understanding the process before and after
major earthquakes. For this purpose, stress-dependent laws in statistical
seismology can be used: the Gutenberg-Richter frequency-size law and the
Omori-Utsu aftershock-decay law. We review the results obtained by using these
laws in previous studies to show a zone of high stress near the eventual
epicenters of the M6.5 and M7.3 earthquakes before the start of the Kumamoto
sequence, and after it, showing a decreasing trend in stress along the
Futagawa-Hinagu fault zone. Detailed analysis suggests aseismic slips along the
causative fault zone. The aseismic preslip locally reduced stress just prior to
the M7.3 earthquake near its epicenter. Recently, a system was proposed by
Gulia and Wiemer (2019) that utilizes the Gutenberg-Richter frequency-size law
to judge, immediately after a large earthquake, whether it was the mainshock or
a foreshock to a future event. Based on the reviewed results and our new
results, further research that takes into account the spatial variation of
frequency-size distribution, allowing the exploration of the possibility of a
local preslip of a future nearby earthquake, is needed to improve this system.
