Slip localization on multiple fault splays accommodating distributed deformation across normal fault complexities

Deformation across structural complexities such as along-strike fault bends may be accommodated by distributed faulting, with multiple fault splays working to transfer the deformation between two principal fault segments. In these contexts, an unsolved question is whether fault activity is equally distributed through time, with multiple fault splays recording the same earthquakes, or it is instead localized in time and space across the distributed faults, with earthquakes being clustered on specific fault splays. To answer this question, we studied the distributed deformation across a structural complexity of the Mt. Marine fault (Central Apennines, Italy), where multiple fault splays accommodate the deformation throughout the change in strike of the fault. Our multidisciplinary (remote sensing analysis, geomorphological-geological mapping, geophysical and paleoseismological surveys) study identified five principal synthetic and antithetic fault splays arranged over an across-strike distance of 500 m, all of which showing evidence of multiple surface-rupturing events during the Late Pleistocene-Holocene. The fault splays exhibit different and variable activity rates, suggesting that fault activity is localized on specific fault splays through space and time. Nonetheless, our results suggest that multiple fault splays can rupture simultaneously during large earthquakes. Our findings have strong implications on fault-based seismic hazard assessments, as they imply that data collected on one splay may not be representative of the behaviour of the entire fault. This can potentially bias seismic hazard calculations.