Seismic heterogeneity and earthquake clustering in the North-Central Chile subduction zone

In subduction zones, seismicity exhibits pronounced space–time heterogeneity that has not been fully explained. While many possible mechanisms, such as frictional heterogeneities, plate geometry, and stress distribution, can lead to contrasting slip behaviors, the precise origin of these slip heterogeneities and their manifestation in space–time distribution of seismicity remain open questions. This is partly due to observational resolution limitations that hinder the detection of fine-scale processes.

For this reason, the north-central zone of Chile is of particular interest: due to the heterogeneities present at the plate interface, associated with the Juan Fernandez Ridge and the Challenger Fracture, where both bathymetric anomalies affect seismic coupling and stress distribution. It is a structurally complex area with abundant seismicity, the occurrence of large interplate earthquakes in recent decades (e.g., the 2015 Mw 8.3 Illapel earthquake and the 1971 Mw 7.8 La Ligua earthquake), and the presence of multiple seismic sequences and persistent seismic activity.

In this study, we conduct a detailed spatiotemporal analysis of seismicity in the North-Central Chile subduction zone, with emphasis on the identification and characterization of seismic clusters using onland seismic time series  from the National Seismological Center (CSN), and from the S5 onland temporary seismic networks , and offshore Distributed Acoustic Sensing (DAS) data , obtained from submarine telecommunications cables (Abyss network), we investigated the nature of these clusters and their possible classification as (foreshock–)mainshock–aftershock sequences, seismic swarms, or repetitive characteristic earthquakes.

By applying deep-learning techniques for seismic phase detection, together with unsupervised learning methods for seismic clustering, we explore the temporal evolution of seismicity and evaluate the existence of unique or recurrent characteristic events through time. Our results aim to elucidate why seismicity in this region is highly heterogeneous and to identify the physical processes that control this variability.