After 5:30 pm on the 21st, there was an earthquake whose epicenter was very deep off the southern coast of the Tokaido, and we observed shaking with a seismic intensity of 3 in Tochigi Prefecture, and observed shaking over a wide range from Tohoku to Kinki.
There was no tsunami caused by this earthquake, and the Japan Meteorological Agency says that the epicenter was so deep that it was a phenomenon called an "abnormal seismic zone" in which shaking was observed over a wide area away from the epicenter.
According to the Japan Meteorological Agency, at around 5:37 pm on the 21st, there was a magnitude 5.8 earthquake with an epicenter at a depth of 380 km off the south coast of the Tokaido.
In this earthquake, the shaking of seismic intensity 3 was observed in Utsunomiya City, and the shaking of seismic intensity 2 and 1 was observed in various parts of Tohoku and Kanto, Nagano and Niigata prefectures, and Wakayama prefecture.
According to the Japan Meteorological Agency, this earthquake seems to have occurred inside the Pacific plate that is subducting from the east of the Pacific Ocean under the Japanese archipelago, so the shaking of the earthquake was transmitted inside the subducting plate. Therefore, it seems that it shook mainly on the Pacific Ocean side, which is far from the epicenter.
The spread of seismic intensity distribution in areas far from the epicenter is called the "abnormal seismic zone".
It is not that the earthquake itself is abnormal, but last month an earthquake occurred deep off the south coast of the Tokaido, and shaking was observed over a wide area.