2,3,2,6,7,10,- 1University Federico II of Naples, DiSTAR - Department of Earth, Environmental and Resources Sciences, Italy (francesco.iezzi@unina.it)
- 2Department of Natural Sciences, Birkbeck College, University of London, UK
- 3School of Geography, Earth and Environmental Sciences, University of Plymouth, UK
- 4Department of Risk and Disaster Reduction, University College of London, UK
- 5Department of Natural Resources Development and Agricultural Engineering, Laboratory of Mineralogy and Geology, Agricultural University of Athens, Athens, Greece
- 6Dipartimento di Scienza e Alta Tecnologia, Universit`a degli Studi dell’Insubria, Como, Italy
- 7Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli Osservatorio Vesuviano, Naples, Italy
- 8Scottish Universities Environmental Research Centre, Glasgow, UK
- 9School of Earth and Environment, University of Leeds, Leeds, UK
- 10Department of Earth Sciences, Durham University, Durham, UK
- 11IGG-CNR Florence, Italy
Slip-rate variations over multiple seismic cycles play a fundamental role in controlling the behaviour of active fault systems, as they are linked to spatio-temporal earthquake clustering and can influence the recurrence patterns of adjacent faults. However, processes that produce slip-rate fluctuations are yet to be fully defined. Despite their importance, the physical mechanisms responsible for such slip-rate fluctuations remain only partially understood. In this study, we investigate whether interactions between neighbouring along-strike brittle faults and their underlying viscous shear zones can generate slip-rate variability associated with synchronous earthquake clustering and fault system synchronization. We focus on nine normal faults and related shear zones within the Central Apennines fault system (Italy), arranged in six along-strike fault pairs characterized by different fault spacings and strike geometries. We integrate cosmogenic 36Cl dating of tectonically exhumed fault scarps with numerical modelling of differential stress transfer between interacting fault–shear-zone pairs. The results identify a mechanism capable of producing simultaneous earthquake clusters, driven by the synchronization of high driving stresses within the viscous shear zones beneath the brittle faults. This behaviour is strongly modulated by along-strike fault spacing and strike variations. In settings with closely spaced fault pairs and limited strike variations, earthquake clusters induce positive differential stress variations on neighbouring shear-zones of sufficient magnitude to induce positive slip-rate variations on their overlying brittle faults. This produces positive feedback mechanism that sustains the occurrence of earthquake clusters that will continue to positively load the neighbouring shear zones. These findings provide new insights into fault system dynamics across multiple timescales and have important implications for seismic hazard evaluation.
How to cite: Iezzi, F., Claudia, S., Roberts, G., Mildon, Z., Robertson, J., Faure Walker, J., Papanikolaou, I., Michetti, A. M., Mitchell, S., Shanks, R., Phillips, R., McCaffrey, K., and Vittori, E.: Structural controls on normal fault synchronization and simultaneous earthquake clustering, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21777, https://doi.org/10.5194/egusphere-egu26-21777, 2026.
