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

Abstract

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 earth- quake 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 earth- quakes is in quasi-periods of decadal or centennial scale. These quasi-periods are related to fault rupture along subduc- tion 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 earth- quakes due to the very long intervals between large magni- tude quakes and the limited historical and scientific records about their characteristics.