Gravity Versus Tectonics: The Case of 2016 Amatrice and Norcia (Central Italy) Earthquakes Surface Coseismic Fractures

Abstract

The 2016 central Apennines earthquake sequence was caused by slip on an extensional fault system and resulted in sizable coseismic surface deformation. The most evident effects occurred along the western slope of Mount Vettore, a geologically and morphologically complex mountain ridge. Steep topography and rheological contrasts are known to have strongly controlled the coseismic deformation pattern during a number of different earthquakes that occurred in mountainous areas worldwide. Nevertheless, so far the role of seismically induced slope failures has not been taken into account in the interpretation of the surface fractures caused by the 2016 earthquake sequence. We modeled the static and dynamic slope stability along the western flank of Mount Vettore and in the underlying Piano Grande plain. Combining the slope stability analysis with geomorphic and geological analyses, we show that the coseismic fractures are distributed along the most unstable areas of the western flank of Mount Vettore and can be partly explained by shaking‐induced mechanisms such as gravity‐driven displacement, compaction, and secondary ground failure. Conversely, in the Piano Grande plain the fracture pattern is not affected by topography or rheology contrasts, suggesting that it is positively caused by tectonic faulting. Different processes, such as gravitational and erosional‐depositional phenomena, may contribute to the exposure of fault scarps during both the coseismic and interseismic periods. Attributing the surface deformation entirely to tectonic faulting, especially in complex mountainous terrains such as the Apennines, may lead to an incorrect assessment of fault displacement and fault slip rate and hence of seismic hazard.

Complex Deformation at Shallow Depth During the 30 October 2016Mw6.5 Norcia Earthquake: Interference Between Tectonic and Gravity Processes?

“…This landsliding could have been reactivated by shaking induced by the stronger and closer M w 6.5 30 October 2016 earthquake, thereby adding some gravity-driven motion to the predominant tectonic slip component. The recent geomechanical model of Di Naccio et al (2019) also heads in this direction, showing that the steep western slope of Monte Vettore is prone to destabilization, in particular due to the presence of tectonic faults marking the contact between lithologies with contrasting mechanical behavior.…”

Partitioning the Ongoing Extension of the Central Apennines (Italy): Fault Slip Rates and Bulk Deformation Rates From Geodetic and Stress Data

“…In the specific case of central Apennines, Kastelic et al (2017) and Stemberk et al (2019) have shown that fault scarps that separate footwall carbonate bedrock from hanging wall carbonate talus, possibly representing the surface extension of upper crustal seismogenic faults, are exhumed also by nontectonic processes, making it hard to detect and quantify the long-term tectonic deformation. Moreover, even surface coseismic ruptures reflect the influence of gravity and rheology, as shown for the 24 August 2016, Amatrice earthquake, and for the 30 October 2016, M w 6.5 Norcia earthquake (Di Naccio et al, 2019;Huang et al, 2017). It follows that discarding as marginal these surficial processes, that is to say, not removing their characteristic signature from the total deformation, may lead to a gross overestimation of the slip per event, and ultimately of the long-term slip rate.…”

Pre-Collapse Space Geodetic Observations of Critical Infrastructure: The Morandi Bridge, Genoa, Italy

“…There is a wealth of scientific literature demonstrating the benefits of InSAR to monitor a wide spectrum of urban processes, such as subsidence [2][3][4][5], foundation settlement [1,6,7], deformation of new buildings [8], surface effects due to tunneling [9][10][11], ground motions associated to faults and local tectonics [12][13][14]. The implementation on real case studies proves the increasing use of these techniques on a routine basis and how they can influence the management of infrastructure assets and preservation of the built environment [1,15,16].…”