A maximum seismic intensity 7 earthquake struck Kumamoto Prefecture on July 28, 2024, causing building collapses and infrastructure failure [1].
The event is significant because the shallow depth of the quake concentrated extreme horizontal force on the surface, leading to severe localized destruction in urban centers.
Damage was reported across several key sites, including the Yatsushiro Castle ruins, and the Nippon Paper Yatsushiro plant [2]. The quake caused a train derailment at JR Yatsushiro Station, the collapse of chimneys, and the uplift of highway sections [1, 2].
Junzo Kasahara, a professor emeritus at the University of Tokyo Earthquake Research Institute, said the earthquake occurred at a relatively shallow hypocenter depth of 16 km [1]. He said that this shallow depth allowed large horizontal shakes to reach the surface directly, resulting in displacement of approximately one meter in some locations [1]. The shaking reached a frequency of about 10 oscillations per second [1].
Seismologists are now focusing on the relationship between two known active faults in the region. According to new data from the Japan Meteorological Agency, the activity zone for these faults appears to be expanding toward the southwest [2].
Experts said that the concentration of damage along the fault line was a direct result of the specific seismic characteristics of this event [1, 2]. The rapid oscillation and high amplitude of the horizontal movement proved particularly destructive to older structures, and transport infrastructure [1].
“The activity zone for these faults appears to be expanding toward the southwest.”
The expansion of the active fault zone toward the southwest suggests that the seismic risk profile for Kumamoto is evolving. Because the damage was driven by high-frequency horizontal shaking from a shallow source, current building reinforcements may need to be re-evaluated to withstand specific lateral displacements rather than just vertical magnitude.
