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A numerical model for the simulation of the seismic cycle in tectonic settings in favor or against gravity: examples from Italy
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  • Matteo Albano,
  • Salvatore Barba,
  • Christian Bignami,
  • Eugenio Carminati,
  • Carlo Doglioni,
  • Marco Moro,
  • Michele Saroli,
  • Salvatore Stramondo
Matteo Albano
National Institute of Geophysics and Volcanology

Corresponding Author:[email protected]

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Salvatore Barba
National Institute of Geophysics and Volcanology
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Christian Bignami
National Institute of Geophysics and Volcanology
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Eugenio Carminati
Sapienza University of Rome
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Carlo Doglioni
Sapienza University of Rome
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Marco Moro
National Institute of Geophysics and Volcanology
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Michele Saroli
National Institute of Geophysics and Volcanology
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Salvatore Stramondo
National Institute of Geophysics and Volcanology
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Abstract

According to the concept of the seismic cycle, earthquakes result from the strain accumulation over a variable decade to millennial period, i.e., the interseismic stage, followed by a sudden stress release, i.e., the coseismic stage, eventually evolving in the postseismic stage. Common analytical and numerical approaches simulate interseismic, coseismic and postseismic stages independently. Often, coseismic models constrain the slip of single or multiple planar sources to fit the available geodetic and InSAR measurements to reproduce fault geometry, slip and regional deformation, regardless the origin of the interseismic forces. We developed a numerical model linking the ongoing interseismic viscous deformation at depth with the coseismic brittle episodic behavior of the upper crust. Our model assumes a brittle upper crust where the fault is locked, and a ductile lower crust, where the fault is steadily shearing. This approach is developed to model typical extensional and compressional earthquakes in Italy including the forces acting during the interseismic period, i.e., the lithostatic load and the horizontal stress field. We adjusted the setup of our model to simulate the interseismic, coseismic and postseismic phases of three seismic events in Italy, two extensional (2009 L’Aquila Mw 6.1 and 2016 Amatrice-Norcia Mw 6.5) and one contractional (2012 Emilia Mw 6). The results of our analysis, compared with the available geodetic and InSAR data, show that the proposed numerical model can reproduce the seismic cycle associated with the investigated events. The modeling provides evidence of interseismic dilatancy above the brittle-ductile transition at the bottom of the locked fault plane in the extensional tectonic setting; coseismic fault motion is triggered by the hangingwall gravitational collapse that recovers most of the interseismic dilatancy formed almost orthogonal to the fault. Vice versa, in contractional tectonic settings, the interseismic horizontal stress accumulates elastic energy in the crustal volume above the bottom of the locked fault; coseismic deformation recovers the elastic energy stored in the hangingwall. The two different settings generate a deformation in favor of gravity in extensional tectonic environments and against gravity in contractional tectonic environments.