Researchers in Japan say a phenomenon known as a slow slip event appears to be occurring at the boundary between tectonic plates located off the eastern coast of Chiba Prefecture, near Tokyo.

The area has been hit by a series of earthquakes since Tuesday. On Friday morning, a magnitude 5.2 quake caused tremors with an intensity of 4 on the Japanese scale of 0 to 7 in Chiba and Saitama prefectures.

Researchers at the Geospatial Information Authority of Japan, which monitors crustal movements using satellite data, say they have been detecting changes in the movements under the Boso Peninsula in Chiba since around Monday.

The researchers say their analyses indicate that a slow slip at the boundary between an ocean plate and a continental plate appears to be underway. They estimate the event has caused a shift measuring up to about 2 centimeters.

Slow slip events were observed off the eastern coast of Chiba six times between 1996 and 2018. Heightened seismic activities were also observed during those six periods.

Professor Nishimura Takuya of the Disaster Prevention Research Institute of Kyoto University analyzed GPS observation data from the Geospatial Information Authority.

Nishimura said the slow slip events off Chiba are expected to continue for seven to ten days. But he added that people need to be vigilant against seismic activity for about a month.

The professor said people should continue to live their lives as usual, but he added that they should be prepared for tremors.