Japan's weather agency has warned of more earthquakes in Chiba Prefecture east of Tokyo following a series of temblors in recent days, detecting a movement known as "slow slip" in tectonic plates off the coast.
The slow-slip event is believed to be occurring off the Boso Peninsula on the boundary between the continental plate and the Philippine Sea plate, according to the Geospatial Information Authority.
An abnormal crustal movement was detected from around Monday. Based on data collected through Wednesday, up to about 2 centimeters of slippage is estimated to have occurred on the plate boundary surface, the organization said Friday.
Earthquakes occur when stress on a fault line or the area between tectonic plates builds up and ruptures. A rapid slide on the fault plane, which usually results in an earthquake, is the release of the strain seen over a period of seconds, whereas a slow slide constitutes movements that can continue for days or even years.
According to the Japan Meteorological Agency, a relative increase in seismic activity has been observed from Monday off the east coast of Chiba Prefecture, including a magnitude-4.9 quake on Thursday and a M5.2 quake on Friday.
Given past quake records in the area, the agency on Friday called on the public to be aware of "strong temblors," citing the possibility of a quake that could register lower 5 on Japan's seismic intensity scale of 7.
Lower 5 is defined as a situation in which people may need to feel the need to hold onto something stable and items on shelves may fall off.
Slow-slip events have also been observed off the Boso Peninsula on six occasions between May 1996 and June 2018, according to the Geospatial Information Authority.
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