ABSTRACT

The 11 March 2011 Tohoku earthquake was the largest seismic event in the history of Japan. Potential mega‐earthquakes were not included in the National Seismic‐Hazard Maps for Japan (NSHMJ) because of the lack of information regarding very infrequent disastrous earthquakes that had occurred before no historical earthquakes were recorded. These earthquakes were not included in the conventional seismic activity model used to assess the probabilistic seismic‐hazard maps (PSHM); however, we recognize that it is essential for the probabilistic seismic‐hazard assessment to consider earthquakes that have a very low probability of occurrence. In order to improve the PSHM, we reconstructed the seismic activity model by (1) revising the long‐term evaluation of magnitude and occurrence probability for large earthquakes; (2) resetting the maximum magnitude of background earthquakes; (3) introducing large area sources to model the background seismicity model for crustal earthquakes; (4) modeling outer‐rise earthquakes; (5) revising the model for large earthquakes in the eastern margin of the Japan sea; and (6) developing new earthquake models for major active faults. Applying these improvements, the revised version of the NSHMJ was published in December 2014 by the Earthquake Research Committee of Japan.

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