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Seismogenic COmpression in southern Italy? – High-resolution topography (Lidar) and mOrphotectonic analySis to test the active nature of the Southern ApenninE Outer Thrust Front

Periodic Reporting for period 2 - COLOSSEO (Seismogenic COmpression in southern Italy? – High-resolution topography (Lidar) and mOrphotectonic analySis to test the active nature of the Southern ApenninE Outer Thrust Front)

Berichtszeitraum: 2020-10-01 bis 2021-09-30

Earthquakes are a major natural hazard in Italy [1]. The bulk of the seismic energy is released along the Apennine belt’s topographic high, where most of the historical- [2] and recent instrumental seismicity [3] nucleates. However, in the last 50 years, moderately energetic sequences (4.0≤Mw≤6.0) with compressional/transpressive sense of motion [4] have unexpectedly occurred also along the external sectors of the Apenninic chain.
Geological, seismic, and morphotectonic evidence of ongoing shortening is reported along the northern- and central Apenninic Outer Front (NAOF and CAOF, respectively), along the Sicilian outer front of the Maghrebian chain and along the Calabrian Arc. On the other hand, orogenic activity along the NW-SE trending Southern Apennines Outer Front (SAOF) is well documented only until the Lower- and part of the Middle Pleistocene (~0.7 Ma) [5, 6]. Nearly 23% of the Italian population is concentrated in southern Italy (https://demo.istat.it). The cost of human losses consequent to earthquakes in Italy (in the last fifteen years) dramatically pointed out the significant vulnerability of the territory [7, 8] even if exposed to moderate magnitude events. This implies a pressing need to fill a gap of understanding on the seismic potential of SAOF, the latter representing about 1/3 of the Apennine outer compressional front.
The COLOSSEO project aims to detect evidence of Late Quaternary (post-125 ka) shortening along the SAOF and document the geometry of possible seismogenic faults. The research strategy envisages a multidisciplinary approach adequate to the peculiar geological-tectonic setting, the SAOF being buried under the Plio-Quaternary foredeep successions [9] and not strongly indicative of recent activity. Tectonic structures belonging to the front are difficult to investigate even because of the low deformation rates (<2 mm/y).
The exploited methodology includes a) analysis of High-Resolution Topography data (e.g. lidar data) to capture fault zone structure and/or offsets; b) assess relative rock uplift rate across the landscape using geomorphic indices from topographic- and fluvial network analysis; c) regional scale field geology; d) seismotectonic analysis exploiting available instrumental seismicity, focal mechanisms and geodetic data.

[1] Gruppo di Lavoro MPS, 2004. http://zonesismiche.mi.ingv.it/; [2] Rovida et al., 2019. https://doi.org/10.13127/CPTI/CPTI15.2; [3] Chiarabba et al., 2016. https://doi.org/10.1111/ter.12233; [4] Montone & Mariucci., 2016. DOI: 10.4401/ag-7235; [5] Patacca, E. and Scandone P. (2004). In: Special Volume of the Italian Geological Society for the IGC 32, 93-129, Florence (2004);[6] Vezzani et al. (2010). DOI: 10.1130/2010.2469; [7] M. Dolce (2004). Seismic safety of schools in Italy. In: Keeping schools safe in earthquakes, Organisation for Economic Co-operation and Development, Paris (OECD, 2004); [8] Ceci et al., 2010. https://doi.org/10.1016/j.engstruct.2009.12.023. [9] CNR, 1992, Structural Model of Italy, Quaderni de La Ricerca Scientifica, 114, sheet 4, scale 1:500,000, S.E.L.CA. Firenze
So far, the research focused along the peri-Adriatic sector of central-southern Italy (Abruzzo-Molise) where the northern SAOF connects (on land) with the CAOF.
Using 10m- px resolution DEM [10] and combining GIS tools (ArcMap by ESRI) with MATLAB-based software [11, 12], local relief- and residual maps, swath profiles, ksn map, and along-river χ-z profiles have been computed in the study area. Results were compared with the main geo-lithological units and structural elements. Fluvial terraces preserved along one of the main river flowing in the study area (Pescara river) have been investigated using 1-to-2m px resolution lidar data (http://www.pcn.minambiente.it/mattm/en/tag/lidar-data/). Seismic reflection sections were also exploited to support a possible correlation between the shortening structures (in the sub-surface) and the pattern of relief- and stream network anomalies (on the surface).
Despite the challenge to test evidence of deformation in this tectonic context, the multidisciplinary approach carried out has been successful and results represent new progress with respect to the state of the art. The main ones can be resumed as follow:

1) EVIDENCE OF LOCALIZED UPLIFT ALONG THE ABRUZZO ADRIATIC PIEDMONT AND ITS INNER FOOTHILL SECTOR - Integration of quantitative geomorphology, topographic analysis and information from the geology allowed to exclude, in the sector, the exclusive lithological influence on the observed anomalies that can be explained with concurrent active shortening along the SAOF (in southern Abruzzo);
2) CONSTRAINTS ON THE LATE QUATERNARY ACTIVITY OF THE SAOF ALONG THE PESCARA RIVER - differential uplift has been observed along the rivers’ terrace treads. This deformation is difficult to explain with long-wavelength regional uplift alone and supports the hypothesis of compressional tectonics throughout the Middle and Late Pleistocene;
3) POSSIBLE ONGOING SHORTENING based on seismicity and historical earthquakes observed in the investigated sector.

The main results achieved so far, both following the activities strictly related to the COLOSSEO targets and also through the promotion of research (on similar thematics) within new-established collaborations, have been disseminated through open-access publications and a dataset [13, 14, 15, 16, 17, 18].

[10] Tarquini et al., 2012. https://doi.org/10.1016/j.cageo.2011.04.018; [11] Schwanghart and Scherler, 2014. https://doi.org/10.5194/esurf-2-1-2014; [12] Forte and Whipple, 2019. https://doi.org/10.5194/esurf-7-87-2019. [13] Ferrarini et al., 2019a. http://doi.org/10.5281/zenodo.4063728; [14] Ferrarini et al., 2019b. doi:10.1130/abs/2019am-338495. [15] Ferrarini et al., 2021a. https://doi.org/10.2113/2021/7866617; [16] Ferrarini et al., 2021b. https://doi.org/10.5281/zenodo.4729624; [17] Ferrarini et al., 2021c. doi: 10.3389/feart.2021.738164; [18] Ferrarini et al. (Eds), 2021d. doi: 10.3389/978-2-88971-361-5
New evidence on Late Quaternary active shortening along the Apenninic Outer Front, in central-southern Italy, and details on the geometry of seismogenic structures may firstly represent a pressing impact on policymakers entrusted with planning strategies.
Nonetheless, in addition to scientific results, the COLOSSEO aims to foster science outreach to society and in particular to young citizens who will be the next successors in the management and planning of the territory and the reduction of risks, including the seismic one.
Within this frame, TREMORs (https://sites.google.com/view/colosseorepository/outreach-tremors) is an educational project being developed and directed to students from Primary and Middle Schools. It aims to 1) promote knowledge of the earthquake as a natural phenomenon, 2) raise awareness of the seismic hazard of the territory 3) promote a resilient coexistence with the associated risk. These activities fully contribute towards the European policy objectives and strategies, in particular to those committed to the reduction of the seismic hazard and in preventing loss of human life and resources by seismic events [19].

[19] Cen (Comité Européen de Normalisation), 2002. Eurocode 8: design of structures for earthquake resistance. Part 1: general rules, seismic actions and rules for buildings. Draft No 5, Doc CEN/T250/SC8/N317, CEN, Brussels, 100 pp.
COLOSSEO project