The magnitude-7.4 earthquake which struck northeastern Japan on Wednesday is likely to have been caused by the temblor at the same location in February 2021, experts say, warning that strong seismic activity should continue in the area.
The powerful quake off the Fukushima coast is considered to be an aftershock of the M9.0 quake in 2011 which devastated the same northeastern region and triggered the nuclear disaster, but its focus was much deeper at 57 kilometers below the seabed than 24 km 11 years ago.
Experts suspect that the quake late Wednesday, which left three people dead and over 180 injured, was directly triggered by the M7.3 temblor occurring at almost the same location at a depth of 55 km on Feb. 13, 2021.
Both quakes registered an upper 6 on Japan's seismic intensity scale of 7 in parts of Miyagi and Fukushima prefectures.
The relationship of the two quakes one year apart is "like a twin," says Takashi Furumura, professor of seismology at the University of Tokyo.
"There is a possibility that part of the fault at that location did not rupture when last year's quake occurred but it did this time with a one-year delay," Furumura said.
Shinji Tooda, Tohoku University's professor of seismology, agrees, saying the parts of fault that ruptured in 2021 and this year sat next to each other and they are "undoubtedly" related.
The quake in February 2021 left over 150 people injured.
The temblor on Wednesday was stronger than the one a year ago in terms of both short and long waves, causing buildings in areas away from the epicenter to shake to an extent that elevators were stopped and a shinkansen bullet train derailed in Miyagi, according to Kojiro Irikura, visiting professor of seismology at Aichi Institute of Technology.
Powerful quakes attributable to a similar fault movement mechanism are likely to continue occurring off the northeastern coast where the Pacific plate meets a continental plate, experts say.
"It is fair to say that intensive seismic activity is resuming in the area," the University of Tokyo's Furumura said.
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