Keywords:Seismic moment conservation principle, Maximum magnitude, Utsu law
Kagan & Jackson [2013, BSSA] estimated maximum magnitude of events which will occur along subduction zone in the world based on the seismic moment conservation principle by applying that to background seismicity from 1977 to 2010. The key point of this method is to replace total seismic moment rate with the tectonic moment rate MT. Note that because the plate coupling rate χ among components of MT has large uncertainty, the maximum magnitude obtained is dependent on χ. To avoid confusion, the magnitude and the seismic moment are represented by “m” and “M”, respectively.They modeled a seismic-moment-frequency-distribution by the truncated G-R law, tapered G-R law and Gamma distribution. These laws have two parameters: β (=b/1.5) and Mc (is characteristic seismic moment which represents the maximum magnitude. Corresponding magnitude is mc). Truncated G-R law do not have events larger than mc. Whereas tapered G-R law and Gamma distribution allow occurrence of events larger than mc. Therefore, it is problematic to treat mc of Tapered G-R law and Gamma distribution as the maximum magnitude.Hirose et al. [2014, SSJ] estimated mc off Tohoku as 9.26 by the truncated G-R law if χ is 60% by applying the seismic moment conservation principle to earthquakes occurred along the Kuril-Kamchatka-Japan trench from 1977 to 2013.There is also Utsu law with upper limit magnitude in addition to the truncated G-R law. In this study, we introduce the formulation of seismic moment conservation principle about Utsu law, and apply it to the same data set as Hirose et al. [2014, SSJ]. As the result, if assumed MT (χ = 60%) is correct, the maximum magnitude of events which will occur off Tohoku in the future is estimated as 10.03. There is a possibility that the Tohoku-oki earthquake is not always the largest event in this area.