The size of local and regional earthquakes in the former Soviet Union (USSR) has been given by the energy class (K-class) system since the late 1950s. K-class was originally developed as a rapid and simple means of estimating the radiated energy (E) from an earthquake and was defined as

K = log10E (in joules).

The nature, origin, and methodology of this system are poorly known to Western seismologists studying Soviet and Russian seismological data, and yet are of great interest and importance to those conducting detailed research on the seismicity of the former...

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