Authorities could have issued a warning over the March 11 earthquake had they treated an earlier quake as a foreshock and closely analyzed the aftershocks that followed, according to a Tohoku University associate professor.
The foreshock, which occurred at 11:45 a.m. on March 9 near the focus of the March 11 quake, some 50 hours before it struck, registered a magnitude of 7.3, rocking Miyagi Prefecture and sending a tsunami of up to 60 cm to Iwate Prefecture.
The Meteorological Agency said this quake might have been a foreshock of the March 11 magnitude 9 quake, whose tsunami ravaged northeastern Japan’s Pacific coast, including Miyagi and Iwate.
Tomoki Hayashino at the university’s Research Center for Neutrino Science analyzed 43 earthquakes with a magnitude of 7.0 or above that occurred around Japan over the past 80 years and checked the number of aftershocks occurring within 20 hours of each.
His research found that the main quakes were followed by zero to two aftershocks with a difference in magnitude from the main shock of less than 1.5 on the scale, and zero to five shocks with a difference of less than 1.7.