Two previously unknown active faults were found off the Boso Peninsula in Chiba Prefecture, with one researcher warning that a jolt in the two faults at the same time could trigger an earthquake of magnitude 8 to 9.
The two faults, one at least 160 km long and the other more than 300 km, were found on the floor of the Pacific Ocean around 100 to 200 km southeast of the southern tip of the peninsula, according to a group of researchers from Hiroshima University, Nagoya University, the Japan Agency for Marine-Earth Science and Technology and other parties.
"The faults have been unmarked and uninvestigated. There is a possibility of strong jolts and tsunami reaching the southern Kanto region (including Tokyo) and the Tokai region (central Honshu). It should be promptly investigated in detail," said research group member Mitsuhisa Watanabe, a professor at Toyo University.