August 12, 2026
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On July 28 at 16:27, an earthquake with a magnitude (M) of 7.1 occurred in the Kumamoto region, Kumamoto Prefecture, at a depth of approximately 15 km. The quake recorded a maximum seismic intensity 7 in Kumamoto Prefecture, where it caused damage. Furthermore, a long-period ground motion of class 4 was also recorded in Kumamoto Prefecture. Its focal mechanism was a strike-slip fault type with a tension axis oriented in the NNW-SSE direction. The earthquake occurred within the Earth's crust.
* Although the number of earthquakes has fluctuated, it is generally declining. Seismic activity remains high, extending across an area of approximately 50 km from NE-SW. As of August 12, at 9:00, the strongest quake recorded was an M6.1 on July 28, at 17:08, whereas 623 earthquakes with a maximum seismic intensity 1 or greater have been recorded.
* Following the M7.1 earthquake, high acceleration values were recorded at several observation stations in Kumamoto Prefecture. These included 1,667 gal at the KiK-net Misumi station and 2,438 gal at the municipal seismic intensity station in Toyono Town, Uki City (both three-component composite).
* GNSS observations revealed that the M7.1 earthquake was accompanied by crustal deformations, which were recorded over a wide area centered on Kumamoto Prefecture. For example, a shift of approximately 87 cm was recorded at the Sencho observation point in Yatsushiro City. Moreover, analysis results from the synthetic aperture radar interferometry of "Daichi 2" and "Daichi 4" satellites provided evidence of significant crustal deformation around the seismic activity area.
* The source fault of the M7.1 earthquake, as inferred from crustal deformation observations, seismic wave analysis, and the distribution of seismic activity is mainly a strike-slip fault oriented in the N-W direction. Its length is estimated to be approximately 30 - 40 km. The largest slip is estimated to have occurred in the northeastern area. The fault slip extends from the rupture initiation point towards shallower depths.
* The seismic activity zone is located near the Futagawa and Hinagu Fault
Zones. This activity is primarily distributed along the Takano–Shirahata
and Hinagu segments of the Hinagu Fault Zone, which is made up of three
parts (the Takano–Shirahata, Hinagu and Yatsushiro Sea segments). The main
part of the M7.1 earthquake's source fault is thought to extend across
the north-eastern part of the Hinagu segment and a portion of the Takano–Shirahata
segment of the Hinagu Fault Zone.
Based on the results of field surveys and aerial photograph analysis, surface seismic faults have been confirmed in the Takano–Shirahata segment of the Hinagu Fault Zone and in the northeastern part of the Hinagu segment. A right-lateral displacement of up to approximately 2 m occurred near Hikawa Town. Moreover, surface seismic faults accompanied by a normal fault component with northwest-dipping displacement have also been confirmed.
GNSS observations indicate that following the M7.1 earthquake on July 28, crustal deformations believed to be post-seismic deformations have been recorded in Kumamoto Prefecture and its surrounding areas, primarily in the southwestern part of the Hinagu segment, Hinagu Fault Zone.
* To the northeast of this seismic activity zone lies the seismic activity zone of the 2016 Kumamoto Earthquake, which extends from the Kumamoto region, Kumamoto Prefecture to central Oita Prefecture. From the Aso region, Kumamoto Prefecture which includes this seismic activity zone, seismic activity has been intense compared to that before the "2016 Kumamoto Earthquake."
* The Earthquake Research Committee assessed that, when active, the Takano-Shirahata and Hinagu segments of the Hinagu Fault Zone have the potential to generate earthquakes with magnitudes of approximately M6.8 and M7.5, respectively. The probability of such earthquakes occurring within 30 years was classified as Rank X (unknown) and Rank S* (high), respectively #2. Furthermore, the probability of an M6.8 or greater earthquake occurring in the southern Kyushu area, including the Hinagu Fault Zone, was estimated to be between 7% and 18%.
* Due to the possibility of earthquakes with a maximum seismic intensity 5 Lower, vigilance is required for about one month. Moreover, the likelihood of earthquakes with a maximum seismic intensity 5 Upper or greater remains higher than the background level of activity. Since this seismic activity zone extends over a wide area and depending on the location and magnitude of subsequent earthquakes, shaking could be stronger than that caused by this one (M7.1). Furthermore, if a large earthquake occurs on the seafloor, caution is required regarding tsunamis.
Note: GNSS refers to a generic term for satellite positioning systems, including GPS.
#1: The 2026 Kumamoto Earthquake (as designated by the Japan Meteorological Agency) refers to the M7.1 earthquake that occurred on July 28, 2026, in the Kumamoto region, Kumamoto Prefecture, and the subsequent series of aftershocks.
#2: Active faults are classified as"S-rank" if the probability of an earthquake occurring within the next 30 years is 3% or higher, "A-rank" if the probability is between 0.1% and less than 3%,"Z-rank" if the probability is less than 0.1%, and"X-rank" if the probability is unknown (meaning that the evaluation is difficult due to insufficient historical earthquake data). An asterisk (*) is appended to the rank for active faults with an elapsed-time rate#3 of 0.7 or greater. Even for Z-rank, the simple existence of the active fault still indicates a possibility that a major earthquake could occur in the area.
#3: A value obtained by dividing the elapsed time from the most recent seismic event by the average recurrence interval at the time of evaluation. This value is 1.0 when the elapsed time reaches the average recurrence interval.