Stress conditions and seismic activity around the rupture zone of the
2016 Kumamoto earthquake in Kyushu, southwest Japan
Abstract
The main events of the 2016 Kumamoto earthquake in Kyushu were a
foreshock (Mw 6.2) on 14 April and the main shock (Mw 7.0) on 16 April
2016, both of which were caused by fault ruptures near the intersection
of the Futagawa and Hinagu fault zones. However, not all sections of the
two fault zones were ruptured during the earthquake. In particular, the
northernmost (Takano-Shirahata) section of the Hinagu fault zone
ruptured, but the rupture did not propagate to southern sections of the
fault zone. We examined fault geometry and paleoseismological data of
the fault zones, and furthermore used numerical analyses to investigate
rupture conditions around the source faults of the earthquake, which
together allowed us to consider the potential for future earthquakes in
the region. Fault geometry, slip tendencies, and fault rupture history
indicated that the rupture potential on the source faults was high
before the earthquake. Seismicity and rupture propagation during the
earthquake sequence were probably controlled by geological
heterogeneities of the fault zones. Coulomb stress change analysis
indicated that stress transfer from the source faults to the Hinagu
section during the earthquakes was smooth, and that most of that section
received a positive stress change. This stress change and the high slip
tendencies we calculated for the Hinagu section indicate that it has
high potential for a future rupture. These results provide crucial
information for preparation for disaster mitigation of future
earthquakes around the rupture zone of the 2016 Kumamoto earthquake.