Earthquake Size Distributions of Strong Worldwide Seismicity Are Similar for Background and Triggered Events

Abstract The size distribution of earthquakes is well described by an exponential law, with its unique parameter called “b-value” in seismology. Several studies indicate that this parameter varies across stress regimes, tectonic settings, and focal mechanisms of earthquakes. Seismic events are usually classified into two types: background earthquakes, that is, events that happen spontaneously as an effect of tectonic loading; and triggered earthquakes, that is, events that are triggered by previous earthquakes. A key question, with huge implications in seismic forecasting, is if the two categories of earthquakes have the same b-value. In seismology, algorithms that can separate these two types of seismicity are called declustering methods. In this work, using a global catalog of strong events and a stochastic declustering method, we demonstrate that background and triggered seismicity have similar b-values. This implies that the b-value reflects intrinsic properties of the faults or the crustal material, rather than the mechanism responsible for the type of event.