‘Slow slip’ activity off Japan’s northeast coast raises fears of major quake

A “slow slip” crustal movement has been detected off the Sanriku coast in northeastern Japan, the same phenomenon observed before the 2011 Great East Japan Earthquake, raising concerns about a possible major quake, Japanese media reported.

Since April, seismic activity across Japan has significantly increased, with more than seven earthquakes of intensity “lower 5” or above recorded. A powerful 7.7-magnitude quake struck the Sanriku offshore area in April, with an extremely shallow focal depth and unusually widespread shaking.

The Japan Earthquake Research Committee confirmed that the slow slip phenomenon – a slow movement of faults that releases strain – is currently accelerating off the Sanriku coast. While such slow release can temporarily reduce local pressure, the released energy may be transferred to nearby fault zones, potentially triggering a larger earthquake.

Experts warned of a chain reaction between crustal activity off Sanriku and seismic activity off Hokkaido, Nemuro and Kushiro. The Itoigawa-Shizuoka tectonic line, a key fault dividing eastern and western Japan, has also been shaking frequently, heightening the risk of a super earthquake in the Nankai Trough.