The two strong earthquakes that hit western Japan on Sunday night left 42 people injured in 10 prefectures and apparent tsunami flipped 14 moored fishing boats in Mie Prefecture, according to the National Police Agency.
Four of the victims were seriously injured, the NPA said Monday.
The two quakes, with preliminary magnitudes of 6.9 and 7.4, struck western Japan in the space of around five hours, prompting residents in some Pacific coastal areas to evacuate amid a tsunami alert.
The quakes originated about 30 to 40 km apart and more than 100 km off the Pacific coast, the Meteorological Agency said.
The first earthquake struck at 7:07 p.m. and the second at 11:57 p.m. This was followed by an aftershock at around 5:31 a.m. Monday with a preliminary magnitude of 5.7, the agency said.
A 86-cm tsunami was reported in Kushimoto, Wakayama Prefecture, and one of 56 cm in Owase, Mie Prefecture. All wave warnings were lifted by 2:40 a.m. Monday.
More than 5,000 people in Wakayama, Mie and other prefectures were temporarily evacuated.
Some people tumbled down stairs or were hit by falling objects, causing broken bones and other injuries. There were also reports of people trapped in elevators and of water pipes rupturing.
Fishing boats capsized in Owase harbor, while around 600 homes were blacked out in the city of Wakayama. A fire broke out at a factory in Sakai, Osaka Prefecture, because of a leak of molten zinc.
The government set up a liaison office at the crisis management center at the prime minister’s office just past midnight to coordinate communications between local authorities and government offices.
“Both earthquakes are believed to have been due to subduction of the crustal plate under the Philippine Sea,” the Meteorological Agency said in a statement early Monday. “This is a situation we have never experienced before.”
Subduction is a process in which one edge of a crustal plate is forced sideways and downward into the mantle below another plate.
The quakes surprised experts who have been predicting a magnitude 8 temblor in the region but under a different mechanism.
It was the first time since the December 1944 Tonankai Earthquake for quakes of this magnitude to occur in rapid succession off the Kii Peninsula, according to the agency.
More than 1,200 lives were believed lost in that magnitude 7.9 temblor.
The epicenter of Sunday’s first earthquake was 110 km east-southeast of Shiono Cape at the tip of the Kii Peninsula. The focus was 10 km below the seabed. The second quake originated 10 km below the seabed some 130 km east of Cape Shiono.