Japan's weather agency said Saturday that no unusual geological strains or movements have been observed in western Japan following a magnitude 7.1 earthquake in the country's southwest, which prompted the agency to issue its first-ever advisory on the increased risks of a potential megaquake in the Nankai Trough.
The findings came from three monitoring points in Kochi and Ehime prefectures, areas projected to be impacted by a potential megaquake in the Nankai Trough, which runs along the Pacific coast, according to the Japan Meteorological Agency.
The focus of the M7.1 quake that rattled southwestern Japan on Thursday was located in waters off Miyazaki Prefecture, on the western edge of the Nankai Trough.
As of 2 p.m. Saturday, 16 quakes measuring 1 or higher on the Japanese seismic intensity scale of 7 have occurred, all with epicenters near waters off Miyazaki, the agency said.
The Nankai Trough is an ocean-floor trench that runs along the Pacific coast where the Eurasian and Philippine Sea tectonic plates meet.
Even though most epicenters are offshore and many inland tremors may be too weak to be felt by humans, seismometers show that activity remains high, according to an agency official.
The agency is urging the public to remain on alert for about a week, as the likelihood of a larger quake striking within this period has been increased to "about one in several hundred."
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