Multi-methodological geophysical characterization for the preservation of Cultural Heritage in seismic area: the case of Museo della Castellina in Norcia (Central Italy)

Historical buildings’ preservation is one the toughest challenges addressed by geoscientist in the field of Cultural Heritage as edifices’ state of conservation should be frequently monitored. This procedure becomes even more urgent in regions characterized by seismic events, since medium-to-high magnitude earthquakes might determine significant and expensive damages. The most common effects of degradation can be investigated with geophysical methodologies since both chemical weathering and mechanical deterioration generally ensure sufficient contrasts of the surveyed physical parameters (e.g. electrical resistivity and relative permittivity). In particular, Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) methods are commonly selected for their logistical simplicity, still granting high resolution results relatively quickly [1] with a non-destructive approach. The case study here presented involves Castellina Museum, an important medieval building in the city of Norcia (Umbria region, Central Italy). Being situated in an active seismic area, this edifice has faced several reconstructions due to the medium-to-high magnitude earthquakes occurred in the last centuries like in the case of 2016-2017 Central Italy seismic sequence when a 6.5 M_w mainshock [2] caused fatalities and damages to the buildings around Norcia. Therefore, to evaluate both the state of conservation and potential aftershocks damages, multi-methodological non-destructive geophysical surveys were conducted over a significant internal masonry wall which location, according to historical documentations, suggests its correspondence to the façade of a previous building, named “Palazzo del Podestà”. An intensive GPR campaign was carried out to evaluate the geometrical arrangement of constructive elements forming the medium. First results provided a peculiar GPR signature, confirming the expected heterogeneous texture and size of such blocks, similarly to the exposed sectors of the wall. However, from the basal floor, electromagnetic signal attenuation occurred over a large portion of the wall. Therefore, ERT was then employed to investigate the variation of electrical parameters [3]. This survey confirmed that the area affected by strong electromagnetic attenuation, are also characterized by electrical resistivity values significantly lower than the ones of neighbouring zones. Therefore, further investigations are needed to better understand the reasons behind this process. This study underlines the importance of employing complementary geophysical methods to achieve a deeper understanding of the studied problem improving the quality of the interpretation needed to define strategic planes for preservation of Cultural Heritages buildings.

 

Reference

[1] Ercoli, M.; Brigante, R.; Radicioni, F.; Pauselli, C.; Mazzocca, M.; Centi, G.; Stoppini, A. Inside the Polygonal Walls of Amelia (Central Italy): A Multidisciplinary Data Integration, Encompassing Geodetic Monitoring and Geophysical Prospections. Journal of Applied Geophysics 2016, 127, 31–44, doi:10.1016/j.jappgeo.2016.02.003.

[2] Porreca, M.; Minelli, G.; Ercoli, M.; Brobia, A.; Mancinelli, P.; Cruciani, F.; Giorgetti, C.; Carboni, F.; Mirabella, F.; Cavinato, G.; et al. Seismic Reflection Profiles and Subsurface Geology of the Area Interested by the 2016–2017 Earthquake Sequence (Central Italy). Tectonics 2018, 37, 1116–1137, doi:10.1002/2017TC004915.

[3] Leucci, G. Ground Penetrating Radar: The Electromagnetic Signal Attenuation and Maximum Penetration Depth. Scholarly Research Exchange 2008, 2008, 1–7, doi:10.3814/2008/926091.