(Guest post by Professor Yuji Yagi)
A destructive earthquake (MJMA 7.3) occurred on 15 April 2016 (UTC) in Kumamoto region, Kyushu Island, Japan. Two day preceding the Kumamoto earthquake, the largest foreshock (MJMA 6.5) occurred on 14 April. And aftershock activity of the Kumamoto earthquake is very high and its distribution implicated that the rupture of mainshock propagated along the complex faulting zone. The source model of the mainshock, in particular, may help to understand the seismicity evolution during the 2016 Kumamoto earthquake sequence in its geologic context.
Yagi et al. 2016 estimated the robust spatiotemporal slip-rate distribution of the 2016 Kumamoto earthquake using the waveform inversion of seismic waveforms, and examined the 2016 Kumamoto earthquake sequence, including the foreshock and aftershock activity. The foreshocks started in the northern part of the Hinagu fault, and the rupture of the mainshock initiated at the junction between the Hinagu and the Futagawa fault zones. The dynamic rupture of the mainshock mainly propagated 30 km northeastward from the epicenter, along the Futagawa fault. The rupture of the mainshock decelerated and terminated near the southwest side of the Aso volcano, and aftershock activity was low around the northeastern edge of the major slip area (where shear stress was increasing due to the coseismic slip of the mainshock). The high temperature area around the magma chamber of Mt. Aso may contribute to the termination of the rupture during the mainshock and peculiarly low aftershock activity of the 2016 Kumamoto earthquake, around Mt. Aso.