Physics – Geophysics
Scientific paper
2011-12-22
Physics
Geophysics
15 figures, 3 tables
Scientific paper
We consider three issues related to the 2011 Tohoku mega-earthquake: (1) how to evaluate the earthquake maximum size in subduction zones, (2) what is the repeat time for the largest earthquakes in Tohoku area, and (3) what are the possibilities of short-term forecasts during the 2011 sequence. There are two quantitative methods which can be applied to estimate the maximum earthquake size: a statistical analysis of the available earthquake record and the moment conservation principle. The latter technique studies how much of the tectonic deformation rate is released by earthquakes. For the subduction zones, the seismic or historical record is not sufficient to provide a reliable statistical measure of the maximum earthquake. The moment conservation principle yields consistent estimates of maximum earthquake size: for all the subduction zones the magnitude is of the order 9.0--9.7, and for major subduction zones the maximum earthquake size is statistically indistinguishable. 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. The long-term rate estimates indicate that, 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.
Jackson David D.
Kagan Yan Y.
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