Expect 3/11 aftershocks for decades

JIJI

Aftershocks of the giant earthquake of March 11, 2011, are expected to continue for at least several decades along the border of Fukushima and Ibaraki prefectures, according to a study released Wednesday.

Aftershocks, including those that can’t be felt by people, are likely to persist for two years off the Miyagi coast and about four years in Tokyo, according to the study by Shinji Toda, an associate professor at Kyoto University’s Disaster Prevention Research Institute.

The findings will be reported to the Japan Geoscience Union Meeting 2012 in Chiba Prefecture next Tuesday.

According to the Meteorological Agency, some 600 aftershocks with an estimated magnitude of 5.0 or stronger were observed extensively in Japan in the year following the Great East Japan Earthquake, the strongest recorded temblor in the nation’s history.

In 2011, the number of earthquakes that measured at least 1 on the Japanese seismic intensity scale to 7 stood at 9,723, four to eight times the number in any of the previous 10 years.

In the study, which covered areas hit by an increased number of quakes after March 11, 2011, Toda calculated how long it will take for the frequency of jolts to return to an average level based on observation data.

Although his modeling showed 800 years or more for the Fukushima-Ibaraki border, Toda concluded the period should be “at least several decades,” given that plates in the March 11 quake’s focal zone will adhere with each other and become less likely to cause shaking.