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Seismic sources and stress transfer interaction among axial normal faults and external thrust fronts in the Northern Apennines (Italy): A working hypothesis based on the 1916–1920 time–space cluster of earthquakes

In this study we analyse the main potential seismic sources in some axial and frontal sectors of the Northern Apennines, in Italy. This region was hit by a peculiar series of earthquakes that started in 1916 on the external thrust fronts near Rimini. Later, in 1917–1921, seismicity (up to Mw≈6.5) sh...

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Bibliographic Details
Published in:Tectonophysics 2016-06, Vol.680, p.67-89
Main Authors: Bonini, Marco, Corti, Giacomo, Donne, Dario Delle, Sani, Federico, Piccardi, Luigi, Vannucci, Gianfranco, Genco, Riccardo, Martelli, Luca, Ripepe, Maurizio
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Language:English
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Summary:In this study we analyse the main potential seismic sources in some axial and frontal sectors of the Northern Apennines, in Italy. This region was hit by a peculiar series of earthquakes that started in 1916 on the external thrust fronts near Rimini. Later, in 1917–1921, seismicity (up to Mw≈6.5) shifted into the axial zone and clearly migrated north-westward, along the belt of active normal faults. The collection of fault-slip data focused on the active normal faults potentially involved in this earthquake series. The acquired data allowed us to better characterize the geometry and kinematics of the faults. In a few instances, the installation of local seismic networks during recent seismic sequences allowed the identification of the causative faults that are hinted to be also responsible for past earthquakes, particularly in the Romagna region and north-eastern Mugello. The Coulomb stress changes produced by the historical earthquakes generally brought closer to failure all the faults that supposedly caused the main seismic events of 1916–1921. However, the stress change magnitude is generally small and thus the static stress interaction among the main seismic sources is not supported by a significant seismic correlation. Significant stress change loading may be instead inferred for the triggering of a number of seismic events on neighbouring normal faults by the Garfagnana 1920 earthquake. In addition, the computation of the seismic stress changes suggests that seismic events with magnitude≥6 may transmit stresses from the axial normal faults to specific external thrusts and vice versa. It is possible that a correlation may be made between loading applied by the major 1917–1920 extensional ruptures and the increased seismicity on the distal external thrusts. •We investigate the seismic sources in axial and outer zones of Northern Apennines.•We examine the Coulomb stress changes produced by the main earthquakes of 1916–1920.•Stress changes are small but may have contributed to trigger specific earthquakes.•M≥6 quakes transmit stresses from the axial faults to outer thrusts and vice versa.•The major 1917–1920 extensional ruptures loaded the outer thrusts.
ISSN:0040-1951
1879-3266
DOI:10.1016/j.tecto.2016.04.045