Identification and Temporal Characteristics of Earthquake Clusters in Selected Areas in Greece

Abstract

The efficiency of earthquake clustering investigation is improved as we gain access to larger datasets due to the increase of earthquake detectability. We aim to demonstrate the robustness of a new clustering method, MAP-DBSCAN, and to present a comprehensive analysis of the clustering properties in three major seismic zones of Greece during 2012–2019. A time-dependent stochastic point model, the Markovian Arrival Process (MAP), is implemented for the detection of change-points in the seismicity rate and subsequently, a density-based clustering algorithm, DBSCAN, is used for grouping the events into spatiotemporal clusters. The two-step clustering procedure, MAP-DBSCAN, is compared with other existing methods (Gardner-Knopoff, Reasenberg, Nearest-Neighbor) on a simulated earthquake catalog and is proven highly competitive as in most cases outperforms the tested algorithms. Next, the earthquake clusters in the three areas are detected and the regional variability of their productivity rates is investigated based on the generic estimates of the Epidemic Type Aftershock Sequence (ETAS) model. The seismicity in the seismic zone of Corinth Gulf is characterized by low aftershock productivity and high background rates, indicating the dominance of swarm activity, whereas in Central Ionian Islands seismic zone where main shock-aftershock sequences dominate, the aftershock productivity rates are higher. The productivity in the seismic zone of North Aegean Sea vary significantly among clusters probably due to the co-existence of swarm activity and aftershock sequences. We believe that incorporating regional variations of the productivity into forecasting models, such as the ETAS model, it might improve operational earthquake forecasting.

Forecasting Strong Subsequent Earthquakes in Greece with the Machine Learning Algorithm NESTORE

“…Considering all these points, several tests were carried out with different available catalogues, and it was found that the Aristotle University of Thessaloniki earthquake catalogue (AUTH) [44] was the most suitable for the time period 1995-2022. This database was also previously used in the study conducted by Bountzis et al (2022) to identify seismic clusters in specific regions of Greece [45].…”

Space-time clustering of seismic events in Chile using ST-DBSCAN-EV algorithm

“…The clustering results provided one relatively large cluster and other small clusters. On the other hand, Bountzis et al [20] present a two step clustering algorithm called the Markovian Arrival Process-(MAP-DBSCAN) to detect change-points in the seismicity rate and subsequently, clustering seismic events in selected areas of Greece. Recently, Sharma [21] proposed two-stage method, based on Self-Organized Map and Density-based Temporal Clustering techniques, for implementing an effective spatiotemporal clustering by identifying the aftershock clusters and background events.…”