Long- and Short-Term Earthquake Forecasts during the Tohoku Sequence

TL;DR

This study analyzes the 2011 Tohoku earthquake sequence, estimating long-term earthquake recurrence intervals and demonstrating the potential for short-term earthquake forecasts based on rate changes, highlighting the need for operational forecasting strategies.

Contribution

It provides a novel analysis of earthquake rate changes before and after the Tohoku earthquake, emphasizing the importance of short-term forecasting during seismic sequences.

Findings

Long-term recurrence interval for M9 earthquakes is about 350 years.

Short-term earthquake rate increased over 100 times before the mainshock.

Post-earthquake rate increased over 1000 times, indicating potential for real-time forecasting.

Abstract

We consider two issues related to the 2011 Tohoku mega-earthquake: (1) what is the repeat time for the largest earthquakes in this area, and (2) what are the possibilities of numerical short-term forecasts during the 2011 earthquake sequence in the Tohoku area. Starting in 1999 we have carried out long- and short-term forecasts for Japan and the surrounding areas using the GCMT catalog. The forecasts predict the earthquake rate per area, time, magnitude unit and earthquake focal mechanisms. Long-term forecasts indicate that the repeat time for the m9 earthquake in the Tohoku area is of the order of 350 years. We have archived several forecasts made before and after the Tohoku earthquake. The long-term rate estimates indicate that, as expected, the forecasted rate changed only by a few percent after the Tohoku earthquake, whereas due to the foreshocks, the short-term rate increased by a factor of more than 100 before the mainshock event as compared to the long-term rate. After the Tohoku mega-earthquake the rate increased by a factor of more than 1000. These results suggest that an operational earthquake forecasting strategy needs to be developed to take the increase of the short-term rates into account.