A regional surface wave magnitude scale for the earthquakes of Russia’s Far East

Abstract

The modified scale M_s(20R) is developed for the magnitude classification of the earthquakes of Russia’s Far East based on the surface wave amplitudes at regional distances. It extends the applicability of the classical Gutenberg scale M_s(20) towards small epicentral distances (0.7°–20°). The magnitude is determined from the amplitude of the signal that is preliminarily bandpassed to extract the components with periods close to 20 s. The amplitude is measured either for the surface waves or, at fairly short distances of 0.7°–3°, for the inseparable wave group of the surface and shear waves. The main difference of the M_s(20R) scale with the traditional M_s(BB) Soloviev–Vanek scale is its firm spectral anchoring. This approach practically eliminated the problem of the significant (up to–0.5) regional and station anomalies characteristic of the M_s(BB) scale in the conditions of the Far East. The absence of significant station and regional anomalies, as well as the strict spectral anchoring, make the M_s(20R) scale advantageous when used for prompt decision making in tsunami warnings for the coasts of Russia’s Far East.