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

The transformation to equivalent dimensions that offers a novel approach for investigating earthquake clustering was engaged to analyze the preparatory phase of the 2020 Samos, Greece, Mw7.0 main shock. The analysis considered earthquakes that occurred between 2006 and October 2020, covering an area extended three times the length of the main rupture. Each earthquake was parameterized by its magnitude, the interevent time (interval since the previous earthquake), and the interevent spatial distance (distance between the epicenters of consecutive earthquakes). Transforming these parameters into equivalent dimensions allowed them to be directly compared. The degree of clustering was quantified using the average distance between earthquakes in this transformed parameter space, calculated within consecutive 100 events data windows. Results revealed a distinct pattern, 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 earthquake clustering in the used parameter space. Beginning from a two-cluster system, when the distance was minimal, the clustering development continued along two branches and ended before the main shock with the formation of five earthquake clusters of different characteristics.