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An analysis suggests that the magnitude-7.2 earthquake that struck off the coast of Iwate Prefecture, Japan, last month may be linked to a "slow slip" phenomenon. Experts urged particular caution, saying the possibility of an even larger earthquake cannot be ruled out.
According to NHK on the 2nd (local time), Professor Naoki Uchida of the Earthquake Research Institute at the University of Tokyo analyzed that a "slow slip" phenomenon — in which the boundary between tectonic plates gradually slides — appears to have been active prior to the magnitude-7.2 earthquake that occurred off the coast of Iwate Prefecture, Japan, on the 25th of last month.
A slow slip refers to a crustal movement in which one plate slowly slides beneath another along a crustal boundary. Unlike ordinary earthquakes, it proceeds relatively gently and produces almost no shaking perceptible to people, but it has been identified as a cause of chain earthquakes or large-scale quakes.
Professor Uchida estimated that slow slip activity became more active following the magnitude-7.7 earthquake that occurred off the coast of Sanriku in April. He expressed concern that the area where slow slip occurs may have expanded off the coast of Japan's Tohoku region to the south and west of the epicenter of the 1994 Sanriku earthquake. The Sanriku region has not experienced a large earthquake of comparable magnitude in the roughly 30 years since a magnitude-7.6 strong quake struck in 1994.
Professor Uchida stressed the need for continued preparedness, saying, "We cannot predict what magnitude the next earthquake will be," and "It could be of the magnitude that has occurred so far, or greater."
The reason the academic community is paying attention to this slow slip is the nightmare of the "Great East Japan Earthquake" that shocked the world in March 2011. At that time, the magnitude-9.0 megaquake and giant tsunami caused enormous casualties, with 15,901 dead and 2,519 missing.
Scientists at the time identified that a slow slip at the boundary between the North American Plate and the Pacific Plate in the Pacific Ocean caused the fault to move 30 to 50 meters, and pointed to this as the main culprit behind the magnitude-9.0 megaquake and the giant tsunami.
