At around 4:27 p.m. on the 28th of July, a large earthquake with a magnitude (M) of 7.1 occurred with a hypocenter at a depth of 16 kilometers in Kumamoto Prefecture. According to the Japan Meteorological Agency (JMA), this earthquake recorded a maximum seismic intensity of 7 in Uki City and Hikawa Town, and shaking was observed over a wide area from Kyushu to Chugoku, Shikoku, and Hokuriku regions. "Long-period ground motion," which slowly shakes upper floors of buildings, recorded Class 4, the strongest level. Shaking continued thereafter, with earthquakes repeating approximately 150 times by 5:00 a.m. on the 29th. This is the first time a seismic intensity of 7 was recorded in Japan since the Noto Peninsula Earthquake in January 2024.
Provided by JMA
On the night of the 28th, the Geospatial Information Authority of Japan (GSI) announced that crustal deformation was observed at three reference points: at "Sencho Electronic Reference Point" in Yatsushiro City near the epicenter, moving approximately 84 cm to the northeast; at "Jonan Electronic Reference Point" in Kumamoto City, moving approximately 40 cm to the north; and at "Izumi Electronic Reference Point" in Yatsushiro City, moving approximately 17 cm to the south.
The JMA named this earthquake the "2026 Kumamoto Earthquake." This earthquake has caused major damage, including building collapses and road cave-ins. The National Police Agency, Fire and Disaster Management Agency, and Kumamoto Prefectural Government are rushing to confirm human casualties. At the large commercial facility "Aeon Mall Kumamoto" in Kashima Town in the prefecture, an explosion thought to be related to the earthquake occurred, resulting in multiple casualties as buildings collapsed. Prime Minister Sanae Takaichi stated before 10:00 a.m. on the 29th: "As of 8:30 a.m., there are 13 deaths, including investigations into connection with the disaster." The number of casualties may increase in the future.
According to the JMA's explanation, this earthquake was a strike-slip fault type with a pressure axis in the east-northeast to west-southwest direction. Because the hypocenter was shallow, shaking was severe, and earthquakes repeated thereafter. At a press conference on the evening of the 28th, a JMA official called for caution regarding earthquakes of around seismic intensity 7 for about one week, especially the next 2 to 3 days, as active seismic activity may continue. In addition, it was pointed out that vigilance against heatstroke is also necessary due to continuing extreme heat in the Kyushu region.
In Kumamoto Prefecture, large earthquakes with a seismic intensity of 7 occurred twice in April 2016. The epicenter of this earthquake is close to those, approximately 20 km from the epicenters at that time. Regarding the connection with the earthquake 10 years ago, an official from the JMA stated that "the relationship is unknown at present," but pointed out that "they are similar in that the shallow hypocenters tend to make seismic activity active." Earthquake research experts almost unanimously consider it highly likely that the unruptured section of the active fault that caused the earthquake 10 years ago slipped. There is a risk that earthquakes may recur in the future, requiring strict vigilance.
Provided by JMA
Multiple active faults exist in Kyushu. Among them, the Futagawa Fault Zone moved significantly in the 2016 Kumamoto Earthquake. The epicenter of this earthquake lies at a position extending from this fault zone and entering the Hinagu Fault Zone. Among the three segments of the Hinagu Fault Zone evaluated by the government's Earthquake Research Committee, it has been repeatedly pointed out that most sections remain unruptured except for one portion. This view suggests that stress had continued to accumulate in part of the Hinagu Fault Zone.
According to long-term evaluations by the Earthquake Research Committee, the probability of an earthquake of around M7.5 occurring within the next 30 years near the "Hinagu Segment" of the Hinagu Fault Zone was "nearly 0 to 6%," categorized in the "S Rank," representing the highest probability among active faults nationwide. Chairman Kazushige Obara of the Earthquake Research Committee called for caution regarding earthquakes near the Hinagu Fault Zone at a press conference in April this year prior to the 10th anniversary of the Kumamoto Earthquake. There is a high risk that "unruptured sections" still remain in the Hinagu Fault Zone. There is also a danger that this earthquake may further affect the fault zone and surrounding active faults. Further vigilance is necessary.
Provided by GSI
Provided by GSI
Original article was provided by the Science Portal and has been translated by Science Japan.