Insights Into a Low Angle Normal Fault From a 10‐Year‐Long High‐Resolution Earthquake Catalog: The Alto Tiberina Fault Case Study (Northern Apennines, Italy)

Abstract The Alto Tiberina fault (ATF) in the Northern Apennines of Italy is one of the most extensively monitored low‐angle normal faults (LANFs) worldwide, hosting The Alto Tiberina Near Fault Observatory (TABOO‐NFO). The down‐dip geometry, mechanical properties, and kinematics of the ATF have been revised based on a new 10‐year (2010–2020) earthquake catalog. The dense configuration of TABOO‐NFO seismic network enabled a low detection threshold, resulting in a catalog of almost 100,000 events with M L < 3.9 and completeness magnitude ≈0.1 in M L scale, with high‐resolution hypocentral locations determined using an optimized 1D velocity model and newly estimated static station corrections. The distribution and kinematics of microseismicity within the ATF fault zone confirm the presence of locked portions along the main LANF plane. Stress build‐up in the locked shallow parts of the ATF results in the development of minor antithetic and splay structures with well‐oriented slip planes in the hanging‐wall, hosting small seismic sequences. In the deeper parts of the fault, creep may be facilitated by low‐friction lithologies, which are thought to promote stable slip. Clustering analysis further shows that the seismic activity of the ATF system evolves predominantly as swarms rather than as main shock‐aftershock sequences, highlighting the role of aseismic creep and stress distribution pattern in controlling seismicity. Our findings provide a major insight into the mechanics of LANFs and emphasize the importance of including both the primary fault and its secondary structures in seismic hazard models, with implications for other creeping fault systems worldwide.