The Government Earthquake Research Committee warned that incomplete fault ruptures may trigger earthquakes larger than the recent magnitude 7.1 event in Kumamoto [1].
This warning signals a critical risk for the region, as it suggests that the energy released during the recent quake was insufficient to stabilize the area. The presence of "remaining cracks" means the geological tension has not been fully relieved, potentially priming the region for a more catastrophic event.
The earthquake occurred on July 28, centering near Uki City and Hikawa Town in Kumamoto Prefecture [2]. The event registered a magnitude of 7.1 [1] with a focal depth of approximately 16 kilometers [1]. The highest intensity, a seismic intensity 7, was observed in Uki City and Hikawa Town [1]. By 5 a.m. on July 29, officials had recorded approximately 150 aftershocks [1].
Research by the committee indicates the activity occurred along the Hinagu fault zone, stretching from Mashiki Town to the Yatsushiro Sea [2]. The committee said the fault active during this event spanned approximately 30 kilometers [3].
Experts linked the current activity to the 2016 Kumamoto earthquakes, noting that certain sections of the fault did not fully slip during those events [2]. This lack of complete rupture left residual stress in the crust. One expert said the section that had remained unbroken finally slipped [3].
Despite these findings, some reports vary on the precise link to the 2016 events. While some sources suggest the mechanism of the earthquake is fundamentally the same [3], others said the specific relationship remains unclear at this stage [4].
The committee emphasized the danger of these incomplete ruptures. The Government Earthquake Research Committee said there are parts that remain unbroken, and the possibility that large earthquakes will occur in those areas in the future is quite possible [5].
“The possibility that large earthquakes will occur in those areas in the future is quite possible.”
The identification of "remaining cracks" in the Hinagu fault zone suggests that the 2016 and 2026 seismic events were partial releases of energy rather than total stabilizations. Because the fault did not rupture completely, the accumulated tectonic stress continues to build in specific segments. This creates a geological paradox where a major earthquake does not necessarily lower the risk of future activity but may instead highlight the specific zones where an even larger rupture is inevitable.
