Predicting earthquakes: The Mw9.0 Tohoku Earthquake and historical earthquakes in Northeastern Japan

A magnitude 7.3 foreshock occurred two days before the magnitude 9.0 Tohoku Earthquake. The energy release of earthquakes within two days after the M7.3 earthquake is obviously different from the aftershocks of the Mw9.0 earthquake. But guided by historical earthquake experience, seismologists regarded the M7.3 earthquake as the main shock rather than a foreshock of another greater earthquake. Based on the analysis of historical earthquakes in coastal areas of northeastern Japan, the recurrence time of earthquakes is in quasi-periods of decadal or centennial scale. These quasi-periods are related to fault rupture along subduction zones located in marine environments adjacent to the coast. The probabilistic prediction for future earthquakes made by Japanese seismologists using historical earthquake data is based on a decadal scale quasi-period. It is difficult, however, to make relatively reliable predictions about the recurrence interval of rare great earthquakes based on historical earthquakes due to the very long intervals between large magnitude quakes and the limited historical and scientific records about their characteristics.