Abstract

We propose a conversion method from alarm‐based to rate‐based earthquake forecast models. A differential probability gain forumla is the absolute value of the local slope of the Molchan trajectory that evaluates the performance of the alarm‐based model with respect to the chosen reference model. We consider that this differential probability gain is constant over time. Its value at each point of the testing region depends only on the alarm function value. The rate‐based model is the product of the event rate of the reference model at this point multiplied by the corresponding differential probability gain. Thus, we increase or decrease the initial rates of the reference model according to the additional amount of information contained in the alarm‐based model. Here, we apply this method to the Early Aftershock STatistics (EAST) model, an alarm‐based model in which early aftershocks are used to identify space–time regions with a higher level of stress and, consequently, a higher seismogenic potential. The resulting rate‐based model shows similar performance to the original alarm‐based model for all ranges of earthquake magnitude in both retrospective and prospective tests. This conversion method offers the opportunity to perform all the standard evaluation tests of the earthquake testing centers on alarm‐based models. In addition, we infer that it can also be used to consecutively combine independent forecast models and, with small modifications, seismic hazard maps with short‐ and medium‐term forecasts.

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