The Hyūga Sea is located at the southwestern end of the Nankai Trough, an active subduction zone. The Nankai Trough represents the plate boundary where the Philippine Sea plate subducts beneath the Eurasian plate. The area is associated with large earthquakes in 1662 (Mw 7.9), 1941 (Mw 8.0), 1961 (Mw 7.5),[3]1968 (Mw 7.5) and two in 1996 (Mw 6.6[4] and 6.7[5]). The Hyūga Sea is interpreted as a transition zone between the highly coupled Nankai Trough in the northeast and weakly coupled Ryukyu Trench further southwest.[6] The 1968 and 1996 earthquakes were subduction zone events occurring on the plate boundary. The 2016 Kumamoto earthquakes were about 140 km (87 mi) northwest of the 2024 Hyūga-nada earthquake and were caused by a similar subduction zone.[2] About 2 km (1.2 mi) beneath the seafloor, low-frequency earthquakes, occur near the shallow subduction interface. Beneath the east coast of Kyushu, on the deeper part of the subduction zone, slow slip events were detected between 1996 and 2017.[7]
The earthquake injured at least 16 people, three of them in a serious condition, collapsed or severely damaged three houses and damaged 77 others across Kyushu.[18] Ten people were injured in Miyazaki Prefecture.[18] In Nichinan, the Obi Castle Town sustained damage. A section of National Route 220 was closed due to rockfalls. A house partially collapsed in Miyazaki, and ten buildings as well as the Miyazaki Airport received minor damage. Two flights each of All Nippon Airways and Solaseed Air were canceled, and some flights of Japan Airlines from the airport were delayed. Water pipe leaks occurred in Kushima. In Kagoshima Prefecture, four people were injured,[18] several walls and a two-story house collapsed, and roads were raised in Ōsaki. A landslide was reported in Shibushi. Two people were injured in Kumamoto Prefecture.[19][20][21][22]
Shinkansen services along the Kyushu and Nishi Kyushu lines were suspended, along with a ferry service from Kobe to Miyazaki. No abnormalities were detected at the Ikata and Sendai nuclear power plants located near the epicenter.[15]
Aftermath
Following the earthquake, the Japan Meteorological Agency (JMA) issued a 'Nankai Trough Earthquake Extra Information' advisory[23] that the probability of a megathrust earthquake along the Nankai Trough increased from a 0.1% per week to 1% chance[24] in what was the first advisory of its kind but clarified that it was not imminent.[10][25] While the JMA stated that no abnormal changes were observed by strain meters, they still maintained the advisory through at least August 14.[26] The JMA called for those living in areas expected to be impacted by a Nankai megathrust earthquake to follow disaster prevention measures provided by the government,[27] and advised households with children, elderly, or physically disabled individuals to consider voluntarily evacuating.[28] The Japanese government designated 707 municipalities in 29 prefectures, including Yokohama, Shizuoka, Hamamatsu, Nagoya, Kyoto, Osaka, Kobe, Okayama, Hiroshima, all of Shikoku, Miyazaki, and parts of Okinawa, as areas at risk of being affected by a strong tremor with an intensity of lower 6 or higher and a tsunami with a height of more than three meters.[29] The warning was eventually lifted on 15 August after the JMA said it had not detected major seismic activity.[30]
Several hotel booking cancellations were reported across Japan due to the advisory, with at least 150 cancellations recorded in Miyazaki,[34] 200 at the Dōgo Onsen in Matsuyama, and over 9,400 participants cancelling their participation in the Yosakoi Matsuri in Kōchi. Many of these cancellations coincided with the Obon holiday week.[35]
^Asano, Youichi; Obara, Kazushige; Matsuzawa, Takanori; Hirose, Hitoshi; Ito, Yoshihiro (2015). "Possible shallow slow slip events in Hyuga-nada, Nankai subduction zone, inferred from the migration of very low frequency earthquakes". Geophysical Research Letters. 42 (12): 331–338. Bibcode:2015GeoRL..42..331A. doi:10.1002/2014GL062165.
^Ioki, Kei; Yamashita, Yusuke; Kase, Yoshihiro (2023). "Effects of the Tsunami Generated by the 1662 Hyuga-Nada Earthquake off Miyazaki Prefecture, Japan". Pure and Applied Geophysics. 180 (6): 1897–1907. Bibcode:2023PApGe.180.1897I. doi:10.1007/s00024-022-03198-3. hdl:2433/284057.
^"日向灘の地震の最大震度別地震回数表"(PDF) (in Japanese). Japan Meteorological Agency. Retrieved 14 August 2024.
^ abc宮崎県日向灘を震源とする地震による被害及び消防機関等の対応状況（第１１報） [Damage caused by the earthquake centered in Hyuga-Nada, Miyazaki Prefecture and the response of firefighting agencies (11th report)] (PDF). fdma.go.jp (in Japanese). 15 August 2024. Archived from the original(PDF) on 15 August 2024. Retrieved 15 August 2024.
^【被害】宮崎 日南市で2人けが 各地で住宅被害も [Damage: Two people were injured in Nichinan City, Miyazaki, Japan, and damage to houses in various areas.] (in Japanese). NHK. 8 August 2024. Retrieved 8 August 2024.
^最大震度6弱を観測 宮崎県内の地震被害まとめ（午後６時半時点） [Summary of earthquake damage in Miyazaki Prefecture (as of 6:30 p.m.), with a maximum intensity of 6] (in Japanese). TBS. 8 August 2024. Retrieved 8 August 2024.
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