▲ The fault area near the strong earthquake that occurred on the 28th
The magnitude 7.1 strong earthquake that struck near Uki City in Kumamoto Prefecture, western Kyushu, on the 28th is pointed to as being caused by the reactivation of the fault that triggered a strong earthquake in the region 10 years ago.
According to analyses by earthquake experts reported by the Asahi Shimbun and Yomiuri Shimbun on the 29th, this strong earthquake is presumed to have been caused by the activity of the Hinagu fault zone, which triggered a magnitude 6.5 earthquake on April 14, 2016.
The Hinagu fault zone is a fault zone approximately 81 km long that connects mountains in a northeast-to-southwest direction, stretching from Mashiki-machi, Kumamoto Prefecture, to the Yatsushiro Sea to the west.
The Japanese government's Earthquake Research Committee previously projected early this year that a magnitude 7.5 earthquake could occur in the land section of the Hinagu fault and a magnitude 7.3 earthquake in the Yatsushiro Sea section, noting that if this fault zone becomes active as a whole, a powerful earthquake of magnitude 8.0 could occur.
At that time, the committee estimated the probability of an earthquake occurring in this region within 30 years to be up to 6%, which Yomiuri explained corresponds to an "S grade," the highest earthquake probability among active faults across Japan.
Earthquakes caused by active faults are known to cause massive damage, such as building and soil collapses, by triggering intense shaking on the ground because the hypocenter depth is relatively shallow.
The hypocenter depth of this strong earthquake was also relatively shallow at 10 km.
During the 2016 Kumamoto strong earthquake, a magnitude 6.5 earthquake originating from the Hinagu fault was followed two days later by a strong earthquake of magnitude 7.3, resulting in about 270 deaths.
At that time, the second magnitude 7.3 earthquake was pointed to as being caused by the Futagawa fault, which extends from the mountainous area in the center of Kumamoto Prefecture to the western sea and partially overlaps the Hinagu fault and the northeastern fault zone.
Naoshi Hirata, chairman of the Earthquake Research Committee of Japan, urged, "As seen in the example of the great Kumamoto earthquake 10 years ago, we must be careful of strong shaking comparable to the strong earthquake on the 28th for the next 2 to 3 days."
Kimiyuki Asano, a professor at Kyoto University who investigated the 2024 Noto Peninsula strong earthquake, pointed out, "We must check the fault movements resulting from the 2016 great Kumamoto earthquake and this earthquake to investigate whether the activity of the Hinagu fault zone has ended with this earthquake or is still in a very small part."
The National Institute of Advanced Industrial Science and Technology in Japan previously analyzed that as the force acting on the north of the Hinagu fault zone dissipated at the time of 2016, the southern part of the fault zone became primed to trigger an earthquake next, and the area near Uki City where this strong earthquake occurred corresponds to this.
The Japan Meteorological Agency urged that just as strong earthquakes hovering around magnitude 7 occurred back-to-back within a mere two days during the 2016 Kumamoto earthquake, attention must be paid to the possibility that an even larger earthquake could occur than the initial one.
When the magnitude 6.5 earthquake occurred during the 2016 great Kumamoto earthquake, warnings were issued to "beware of aftershocks," but two days later, a stronger earthquake of magnitude 7.3 occurred, raising criticisms that the term aftershock lowers the sense of alertness against additional damage.
This strong earthquake registered a seismic intensity of 7 on the Japan Meteorological Agency's seismic scale, making it the first time a seismic intensity of 7 has been observed in Japan since the January 2024 Noto Peninsula strong earthquake, which claimed the lives of more than 700 people.
This marks the 8th time that a seismic intensity of 7 has been observed since the 1995 Kobe earthquake, which killed 6,434 people, and 3 of these instances occurred in Kumamoto Prefecture alone.
Due to this strong earthquake, parts of the Kumamoto Castle walls, which had collapsed during the earthquake 10 years ago and were still under repair, collapsed again, dealing another blow to the disaster-stricken area where the scars of past earthquakes had yet to fully heal.
(Photo: Wikipedia capture, Yonhap News)
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