The 1968 Hyūga-nada earthquake (Japanese: 1968年日向灘地震) occurred on April 1 at 09:42 local time. The earthquake had a magnitude of Mw 7.5, and the epicenter was located in Hyūga-nada Sea, off the islands of Kyushu and Shikoku, Japan. The magnitude of this earthquake was also given as MJMA 7.5.[3] A tsunami was observed.[4] One person was killed, and 22 people were reported injured.[2][5] The intensity reached shindo 5 in Miyazaki and Kōchi.
This earthquake is the strongest event recorded in the Hyūga-nada Sea region. The maximum slip was estimated to be 4 m.[7] It was estimated that, in the Hyūga-nada Sea region, earthquakes with magnitudes about 7.6 occur with a period of about 200 years, while earthquakes with magnitudes about 7.1 occur with a period of about 20 to 27 years.[8] It has been pointed out that there is a tendency of occurrence of inland earthquakes in Kyushu before and after large interplate earthquakes in the Hyūga-nada Sea region.[9]
^Yagi, Yuji; Kikuchi, Masayuki (2003), "Partitioning between seismogenic and aseismic slip as highlighted from slow slip events in Hyuga-nada, Japan", Geophysical Research Letters, 30 (2): 1087, Bibcode:2003GeoRL..30.1087Y, doi:10.1029/2002GL015664