Origins and Methodology of the Russian Energy K-Class System and Its Relationship to Magnitude Scales

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 = log10 E (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 USSR. Since its inception, K -class has been the primary means of quantifying the size of small events in the former USSR and continues to be used for that purpose today. In most of this region, scientists employed the method of Rautian (1960), using the maximum horizontal (for the S wave) and vertical (for the P wave) amplitudes, which became the standard for local and regional networks in the early 1960s. In this paper, we describe the origins and basic principles of the energy class system, as well as the methodology generally used today by the regional networks (figure 1) of the states of the former USSR. Shortly after World War II, between 1946 and 1949, three large earthquakes occurred in Soviet Central Asia and triggered an intense study of seismicity. After the magnitude 7.4 Khait earthquake of 10 July 1949, the Geophysical Institute (now the Institute of Physics of the Earth) of the USSR dispatched an expedition to Garm, Tajikistan (figure 1), to deploy a temporary network around the epicentral region. This Complex Seismological Expedition (CSE), which included the senior authors of this paper (Khalturin and Rautian) at its inception, became permanent in 1954. The study of regional seismicity was not well-developed …