Against Båth’s Law: When Aftershocks Became Mainshocks—Implications for Earthquake Forecasting Communication

Abstract

Abstract The Båth’s law is an empirical seismological relation between the magnitudes of the mainshock and the largest aftershock of a seismic sequence. This empirical law, differently from other seismological laws, could be valid only when the seismic sequence is ended. Indeed, during the sequence, we do not know if the strongest event has already happened or not, and then inferring something about the magnitude of the largest aftershock is hazardous. In this opinion article, we discuss some issues related to the Båth’s law: its validity on a global catalog, the use of the terms “mainshock” and “aftershock” in the seismological community and in the public, and their implications in earthquake forecasting communications. We show the uselessness of Båth’s law in earthquake forecasting and that the words “mainshock” and “aftershock” have different interpretations for the public and for seismologists. We argue that their use during an ongoing seismic sequence, without a proper explanation of their meaning, could be confounding, in particular for the Italian language. Calling all events just “earthquakes” could be a simple but effective solution.