Dozens of small shallow-focus quakes hit Nagano Prefecture and its surrounding regions on Tuesday as the weather agency issued an emergency alert for possible strong temblors.
The largest of the quakes, measuring a magnitude 5.3 and a 4 on Japan's intensity scale, hit Takayama in Gifu Prefecture at 1:13 p.m. The city of Takayama said no damage has been confirmed. There were no worries for tsunami.
More than 30 quakes registering 1 to 3 on the Japanese earthquake intensity scale of 7 have been observed in the areas since dawn on Tuesday. Though the magnitude is not large, shallow quakes can cause disproportionately intense shaking.
A total 285 earthquakes that can be felt hit the same areas between Aug. 3 and Nov. 3 in 1998 due to bedrock distortion caused by the diving of the Pacific plate underneath a continental plate. The Japan Meteorological Agency said it is calling on residents to remain alert as a similar mechanism may be behind the latest quakes.
Robert Geller, seismologist and professor emeritus of the University of Tokyo, said: "The energy released by a quake goes up by a factor of 30 for every increase of 1.0 in magnitude, so the small quakes are negligible. Maybe the probability of a large quake is a tiny bit larger right after a small quake, but not to the extent that any special action is warranted."