An experiment on earthquake size distribution estimations reveals unexpected large epistemic uncertainty across methods

The earthquake size distribution is well described by the Gutenberg Richter Law, controlled by the b-value parameter. In recent decades, a great variety of methods for estimating the b-value have been proposed by the scientific community, despite the simplicity of this relationship. All these methods underlie the different views of individual modellers and, therefore, often generate inconsistent results. In this study, we perform a seismological experiment in which we compare different, commonly adopted, methodologies, to estimate the completeness magnitude and the b-value, for seismicity in Central Italy. The intermethod differences are on average equal to 0.4 and 0.3, for Mc and b, respectively, but reach much larger values, especially during more intense seismic activity. This shows that epistemic uncertainty in the b-value plays a more crucial role than intramethod uncertainties, opening new perspectives in the interpretation of discrepant, single studies.