Unveiling the roots of seismogenic faults in central southern Apennines

Transient aseismic processes, driven by fluid movement, fault creeping, and slow slip events, can further influence earthquake distribution, primarily due to tectonic loading. Analyzing seismicity clusters induced by these transient processes is highly valuable for understanding fluid circulation dynamics (De Barros et al., 2021) and unraveling the geological complexities of tectonic structures that influence the spatiotemporal evolution of seismicity within complex fault systems (Ross et al., 2019: de Nardis et al., 2024).

To perform such analysis, it is essential to utilize comprehensive and accurate seismic catalogs with higher spatiotemporal resolution than the standard ones. From this perspective, we analyzed seismic activity in a high-seismic-hazard area of the central-southern Apennines in Italy, characterized by a complex fault network. This region, which has experienced large earthquakes in the past, has remained relatively quiet in recent years.

To explore the spatial relationships between background seismicity, clustered seismicity, and Quaternary geological structures, we examined seismic activity over 37 years (1981–2018) across various crustal depths. The whole dataset was split into three periods with consistent magnitude completeness (1981–2005, 2006–2011, and 2012–2018). For the 2012–2018 period, during which the seismic network configuration was stable, we applied a filter-matching technique to refine the catalog. This analysis identified 72 spatiotemporal clusters and established a baseline seismicity rate. Seismic sequences and swarm activities were distinguished, and their spatial distribution was analyzed concerning active faults, Vp/Vs ratios, and CO2 anomalies.

The seismicity in this area appears to be primarily localized between 10 and 14 km. A noteworthy finding is the absence of significant seismicity at depths < 10 km, which could suggest significant coupling of the shallower faults. These tectonic structures remain locked, preventing fluid ascent, but triggering seismic clusters at greater depths. Our results have helped to constrain some segments of active seismogenic structures at depth, enhancing the understanding of the area's seismogenic potential and seismic hazard, which remains high due to the occurrence of strong seismic sequences in the past.

De Barros, L., Wynants-Morel, N., Cappa, F., & Danré, P. (2021). Migration of fluid-induced seismicity reveals the seismogenic state of faults. Journal of Geophysical Research: Solid Earth, 126, e2021JB022767. https://doi.org/10.1029/2021JB022767

de Nardis, R., Vuan, A., Carbone, L. et al. (2024). Interplay of tectonic and dynamic processes shaping multilayer extensional system in southern-central Apennines Sci Rep 14, 18375 (2024). https://doi.org/10.1038/s41598-024-69118-8.

Ross, Z. E., Trugman, D. T., Hauksson, E. & Shearer, P. M. (2019). Searching for hidden earthquakes in Southern California. Science 364, 767–771.