Abstract

To be unbiased and uniform across a wide geographical area, seismic hazard assessments based primarily on earthquake recurrence rates require that the same magnitude scale be used for all earthquakes evaluated. Increasingly, moment magnitude, MW, is seen as the magnitude of preference. Moment magnitude, however, was not routinely calculated in the past for earthquakes in Canada, necessitating the conversion from other magnitude types in common use. This step is complicated by the fact that several magnitude scales are routinely reported for Canadian earthquakes with the choice being influenced primarily by geography and to a lesser extent by the size of the earthquake. This paper focuses on eastern Canada, where mN is the most commonly used magnitude scale. Conversions to MW are established and evaluated. The simple conversion of applying a constant is sufficient. However, the conversion is time dependent with the constant changing from 0.41 to 0.53 in the mid-1990s.

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