Clustering indications before the Mw7.0 2020 Samos, Greece, main shock as revealed in an equivalent dimensions space

The transformation to equivalent dimensions, which offers a novel approach for investigating seismic processes was engaged in analyzing the preparatory phase of the 2020 Samos, Greece, M_w7.0 main shock. The analysis considered earthquakes between 2006 and October 2020, just before the main shock occurrence, covering an area extended three times the length of the main rupture. The earthquake occurrence times, epicentral geographical coordinates, and magnitudes were used to evaluate triplets comprising the magnitudes, waiting times – the intervals since the previous earthquake, and epicentral offsets – the distances between the epicenters of this and the previous earthquake. After transforming these new parameters into equivalent dimensions, their triplets became points in the [0,1] cube. The points were linked to the times of earthquake occurrences. The average distance between these points, calculated within consecutive 50–event data windows, was used to track the evolution of the seismic process. Results revealed a distinct pattern, in which the average distance was increasing steadily during the twelve-year period before the main shock. These temporal changes in the average distance were driven by a systematic evolution of the {magnitude, waiting time, epicentral offset} points clustering. Similar behavior of the average distance between the {magnitude, waiting time, epicentral offset} points was also observed in other strong earthquake cases. This suggests that tracking the time changes of the average distance between such new parameterizations of the earthquake process may also add, in the future, to earthquake forecasting methods.