Earth Planets Space, Vol. 63 (No. 3), pp. 239-260, 2011
Fuyuki Hirose and Kenji Maeda
Seismology and Volcanology Research Department, Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052, Japan
(Received May 7, 2010; Revised September 28, 2010; Accepted October 15, 2010; Online published March 4, 2011)
The frequency-magnitude distribution expressed by the Gutenberg-Richter (G-R) law is the basis of a simple method to forecast earthquakes. The frequency-magnitude distribution is sometimes approximated by the modified G-R law, which imposes a maximum magnitude. In this study we tested three earthquake forecast models: Cbv (the Constant b-value model) based on only the G-R law with a spatially constant b-value, Vbv (the Variable b-value model) based on only the G-R law with regionally variable b-values, and MGR (the Modified G-R model) based on the modified G-R or G-R law (chosen according to Akaike Information Criterion) with regionally variable b-values. We also incorporated aftershock decay and minimum limits of expected seismicity in these models. Comparing the results of retrospective forecasts by the three models, we found that MGR was almost always better than Vbv; Cbv was better than Vbv for short-term (one year) forecasts; little difference between MGR and Cbv for short-term forecasts; and MGR and Vbv tended to be better than Cbv for long-term (three years or longer) forecasts. We propose the use of MGR in the earthquake forecast testing experiment by the Collaboratory for the Study of Earthquake Predictability for Japan.
Key words: Earthquake forecast, G-R law, modified G-R law, b-value, modified Omori formula, minimum limit of expected seismicity, retrospective forecasts, CSEP for Japan.