Reassessment of the Relationship between M_JMA and Seismic Moment for Inland Earthquakes and Proposal for Subsequent Scaling Laws

Abstract

We first summarize the relationship between the JMA magnitude M_JMA published by the Japan Meteorological Agency and the seismic moment M₀, or the moment magnitude M_W, published by the National Research Institute for Earth Science and Disaster Resilience for earthquakes that occurred in Japan between 1988 and 2024. We report that M_JMA and M_W are equal for plate boundary earthquakes and intra-plate earthquakes, while there is a magnitude-independent noticeable difference only for inland crustal earthquakes. Next, we show how the proposed conversion equation differs from the empirical formulae that have been widely used to obtain M₀ from M_JMA and M₀ or M_JMA from the source length L. Then, by combining the proposed conversion equations with the existing scaling laws for the source area S, we extend the scaling laws for the source length L to be valid over a wide magnitude or M₀ range and show that it is well consistent with recent observations.