Mapping fault dynamics: Very high seismicity detected along the Kefalonia Transform Faul with DAS and template matching

The Kefalonia Transform Fault (KTF), a 150-km long tectonic boundary connecting the Adriatic and Aegean plates, is characterized by slab tearing and significant seismic activity. Earthquake sequences in the region are clustered along the fault, yet the local earthquake catalog records remain sparse.

From April 23 to June 22, 2024, we conducted a two-month Distributed Acoustic Sensing (DAS) experiment on Kefalonia Island using a 15 km dark fiber network—7 km along a roadway and 8 km across the seafloor. By applying the STA/LTA method to marine DAS data, we detected ~10,000 high-frequency (5–20 Hz) events. Event clustering using pairwise correlations, combined with the local earthquake catalog, revealed six spatially distinct seismic clusters, each associated with specific fault segments.

Using these clusters as templates, we developed a new template matching workflow to expand the earthquake catalog to ~20,000 events, significantly increasing the detection of small-magnitude earthquakes. Each cluster highlights seismic activity on distinct fault segments and reveals foreshock and aftershock sequences for ML >2.5 events.

The refined catalog, with 100 times more events than the original local catalog, provides unprecedented temporal and spatial resolution of seismicity along the KTF. These results offer new insights into fault segment interactions and the processes of stress accumulation and release in the KTF system.