According to the Japan Meteorological Agency, at around 4:30 PM on August 8, a magnitude 7.1 earthquake occurred with a depth of 31 kilometers offshore from Hyuga-nada, and a tsunami of 50 centimeters was observed at Miyazaki Port in Miyazaki City, with tsunamis reaching various locations from Kyushu to Shikoku.
Additionally, this earthquake resulted in a seismic intensity of 6弱 (weak 6) being recorded in Nichinan City, Miyazaki Prefecture, and a seismic intensity of 5強 (strong 5) being recorded in Miyazaki and Kagoshima Prefectures.
The Japan Meteorological Agency continues to urge caution for earthquakes with a maximum seismic intensity of around 6弱 for about a week following the earthquake.
In response to this earthquake, the Japan Meteorological Agency announced an “Emergency Information on the Nankai Trough Earthquake (Large Earthquake Advisory),” stating that the likelihood of a major earthquake occurring in the assumed source region of the Nankai Trough earthquake has increased compared to usual.
The agency noted that while the frequency of a magnitude 8 or higher earthquake occurring within seven days after a magnitude 7 or higher earthquake is around once every few hundred times, it does not imply that a major earthquake will definitely occur.
Since the earthquake on August 8, seismic activity has continued in Hyuga-nada and southeast off the Osumi Peninsula, and small-scale seismic activity referred to as “deep low-frequency earthquakes” has also been observed in the Kii Peninsula and Ise Bay, with changes detected by nearby strain meters.
Additionally, small-scale earthquakes known as “shallow ultra-low-frequency earthquakes” have been observed in Hyuga-nada and southeast off Kyushu.
Furthermore, crustal deformation has been observed, particularly in the southern part of Miyazaki Prefecture, and from around the 5th of the month, changes in water pressure believed to be caused by crustal deformation have been recorded by monitoring equipment set up in Kumano-nada.
These phenomena are all occurrences that are regularly observed, and so far, no significant changes in crustal deformation or seismic activity have been observed in the assumed source region of the Nankai Trough earthquake.
The government is calling on the 707 cities and towns in 29 designated prefectures for promoting disaster prevention measures to reaffirm their earthquake preparedness for one week after the earthquake.
Specifically, they are urging people to secure furniture, check evacuation locations, and confirm methods for checking on family members’ safety. It is also suggested that households or facilities with elderly individuals, disabled persons, or small children may require additional time to evacuate, and they should consider voluntary evacuations as necessary.
This government advisory is expected to end at 5 PM on the 15th, one week after the earthquake occurrence.
However, since the Nankai Trough giant earthquake is projected to have a high probability of occurring at 70% to 80% within the next 30 years, continued vigilance is necessary.