The Purpose and Definition of the Minimum Magnitude Limit in PSHA Calculations

A lower limit of magnitude M-min is routinely defined for integrations of earthquake scenarios in probabilistic seismichazard analysis but there is widespread misunderstanding of the technical bases for determining the value of this parameter. In this article, several misconceptions are identified and discarded prior to providing a clear and unambiguous definition of M-min that points to the fact that seismic-hazard assessment is always conditioned by the intended application of the outputs. We argue that Mmin is therefore an engineering parameter that is ultimately related to seismic risk rather than seismic hazard. The confusion surrounding this topic could be largely alleviated by defining lower limits on appropriate intensity measures rather than on magnitudes used as a proxy for shaking levels.