Detrended fluctuation analysis of seismicity and order parameter fluctuations before the M7.1 Ridgecrest earthquake

Detrended fluctuation analysis (DFA) has been recently applied for the investigation of temporal correlations between the earthquake magnitudes before major earthquakes. Here, we employ DFA together with natural time analysis in order to identify precursory phenomena to the M7.1 Ridgecrest earthquake on July 6, 2019. The analysis reveals that a minimum of the variability of the order parameter of seismicity in natural time is observed almost a month before the occurrence of this earthquake. This minimum was observed when DFA indicated the development of the presence of long-range correlations which turned to an almost random behavior before the strong earthquake. Upon starting the study of seismicity in natural time from the minimization of the variability on June 5, 2019, we conclude that criticality has been reached at 22:41 UTC on July 2, 2019, almost 3 days before the earthquake occurrence. The application of an algorithm based on the coherent noise model would have led to a warning 3 min before the occurrence of the M7.1 Ridgecrest earthquake.