April 17, 2016
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Earthquake in Kumamoto Region, Kumamoto Prefecture on April 16, 2016

* On April 16 at 01:25 (JST), there was a magnitude (M) 7.3 (provisional) earthquake at a depth of approximately 10 km in the Kumamoto region, Kumamoto prefecture. This event had a maximum seismic intensity 6 Upper observed in Kumamoto prefecture and caused damage. In this region on April 14 at 21:26, there was a M6.5 (provisional) earthquake at a depth of approximately 10 km and maximum seismic intensity 7 was observed in Kumamoto prefecture. The seismic activity is high. Earthquakes have occurred in the region extending approximately 30 km length in an NE-SW direction and in the surrounding regions of its extension, the Aso region, Kumamoto prefecture and also Oita prefecture.

* The focal mechanism showed a strike-slip fault type with a tension axis in an N-S direction. This event occurred within the crust at a shallow depth. The source fault estimated from the distribution of aftershocks and the focal mechanism of the main shock is a right-lateral strike-slip fault extending in an NE-SW direction.

* Accompanying this event, large acceleration values were observed, such as 1362 gal (synthesis of 3 components) at Masuki observatory of KiK-net in Kumamoto prefecture.

* According to the GNSS observation, crustal deformations associated with this event were observed, such as a displacement of approximately 97 cm (provisional) to the south-west direction at Choyo observatory in Kumamoto prefecture.

* In the vicinity of the focal area, there is the Futagawa fault zone. According to the field survey, surface ground faults were found along the Futagawa segment of the Futagawa fault zone. This event is considered to be due to the activity of Futagawa segment of the Futagawa fault zone. The Earthquake Research Committee evaluated for the Futagawa fault zone (Futagawa segment) that a M7.0 or so earthquake is possible to occur at an active time and the probability value of the earthquake occurrence within 30 years is 0%~0.9% (rather high). In addition, the probability of earthquake occurrence of M6.8 or over for the southern Kyushu area including Futagawa fault zone was evaluated as 18%-27%.

• Earthquake in the Kumamoto Region, Kumamoto Prefecture on April 16, 2016 at 01:25 - Distribution of Seismic Intensities
• Earthquake in the Kumamoto Region, Kumamoto Prefecture on April 16
• The 2016 Kumamoto Earthquake - Seismic Activity in the Area from Kumamoto to Oita Prefectures (as of April 16 at 13:30)
• Comparison of Cumulative Numbers of Aftershocks of Major Earthquakes generated in Inlands and Coasts (including the Main Shocks) (Magnitudes are greater than 3.5)
• Earthquake in the Kumamoto Region, Kumamoto Prefecture on April 16, 2016 - Distribution of Seismic Sources in the Vicinity of the Focal Area
• Strong Ground Motions due to Earthquake in the Kumamoto Region, Kumamoto Prefecture on April 16, 2016
• Observed Data before and after Earthquake (M7.3) (provisional) in the Kumamoto Region, Kumamoto Prefecture on April 16, 2016 (1)
• Earthquake (Mj7.3) in the Kumamoto Region, Kumamoto Prefecture on April 16, 2016 - Seismic Fault Model (provisional)
• Focal Process of Earthquake in the Kumamoto Region, Kumamoto Prefecture on April 16, 2016
• Results of Field Survey of Surface Displacement (1)
• Results of Field Survey of Surface Displacement (2)
• Probability of Earthquake Occurrence for the Futagawa Fault Zone, Hinagu Fault Zone and Beppu-Haneyama Fault Zone