Comment on "Test of seismic hazard map from 500 years of recorded intensity data in Japan" by Masatoshi Miyazawa and Jim Mori

Miyazawa and Mori (2009) propose testing probabilistic seismic hazard assessments (PSHAs) for Japan in terms of predicted macroseismic intensities against those observed over the past 500 yrs. While the comparison presents a real interest to the seismological and engineering communities, their reasoning is based on an incorrect hypothesis and leads to several problems. Comparing probabilistic estimates and observations is an important topic; any available observations should be used to infer constraints on the probabilistic estimates. Testing long-term earthquake hazard predictions is currently one of the biggest challenges in the area of engineering seismology. Several current large-scale seismic hazard projects have work packages dedicated to developing so-called validation techniques (e.g., the European Commission-funded Seismic Hazard Harmonization in Europe [SHARE] project and the Global Earthquake Model). Obviously, this task should be performed with great caution, as such validation studies have a direct impact on, for example, estimates of seismic risk and building regulations.