Abstract

Magnitude-frequency relations are investigated for the on-land area, covered by the Tohoku University seismic network, northeastern Japan. We combine the Japan Meteorological Agency (JMA) catalog with the Tohoku University catalog for the crustal events. The suite for the upper plane events of the double-planed Wadati-Benioff zone, from 60 km through 100 km deep, is based on the Tohoku University catalog only. Completeness analyses of the catalog reveal that the crustal events and the upper plane events suite is complete down to magnitude 2.0 and 2.1, respectively. Including events only with magnitude above the completeness threshold, the magnitude-frequency relations are found to be nonlinear both for the crustal events slightly and the upper plane events strongly. Consistency between total seismic wave duration magnitudes and velocity amplitude magnitudes suggests that the magnitude scale in the catalog is nonbiased. The completeness analyses and the non-biased magnitude scale suggest that the nonlinear magnitude-frequency relations are not artificial but substantial features of the earthquake occurrence.

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