Interaction between transverse and rift faults during the initiation of orogenic extension: the case of Sant'AnnaPelago (Northern Apennines, Italy)

Abstract

Sant'Anna Pelago is located near the extensional front of the Northern Apennines (Italy) between Modena and Lucca, an area characterized by multiple lateral steps of the NW-SE striking tectonic system and orographic divide. The region is affected by significant instrumental seismicity with over a thousand recorded events (0.5 < M < 4.8) from 2006 to 2024, and few 4.13 < Mw < 4.33 historical earthquakes. Nevertheless, it is not clear what are the geometries and kinematics of the faults, nor which are seismogenic, and as a result we have few constraints on how extensional basins initiate and link across their lateral steps. In this study we performed absolute and relative relocation of earthquakes and focal mechanism computation to analyze the most significant seismic sequences. We calculated Coulomb stress changes from the 2013 Mw = 4.8 strike-slip mainshock that occurred on a fault transverse to the Apennines and show that it caused the 2013 aftershock sequence on an overlying, NW-SE striking normal fault. Most of the other sequences occurred on a nearby system of steep, en echelon normal faults. Structural field observations support the existence of a major strike-slip transverse deformation zone extending to the Sant’Anna Pelago area. Our results show that extensional and transverse strike-slip faults can be active synchronously and closely interact through mechanisms such as stress triggering.

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ORCID for Derek Keir: orcid.org/0000-0001-8787-8446

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