Researchers have discovered two active faults in Nagoya, with parts of them running for roughly 5 km just underneath major highways in the metropolis.
The team of researchers from Nagoya University and Hiroshima University warned that the faults, which extend vertically through the city for at least 10 km, "could trigger a magnitude-7-class" or greater earthquake.
"Further investigation is needed," Nagoya University researcher Nobuhiko Sugito said Monday.
The latest findings could affect the city's emergency planning policy, which is not based on the existence of specific faults and assumes that only a quake of a magnitude of 6.9 could hit within the city, even in the case of faults existing directly beneath it.
The researchers analyzed landscapes in central Nagoya using aerial photographs and 3-D images and found land distortions such as cliffs, believed to have been made by fault activity, in wide swaths of the city.
Using existing geological data, they also found changes in the depth of layers, which indicate fault slips. Such changes have been spotted in layers younger than 12,000 years as well as older layers, leading them to believe they are active faults.