Numerical and experimental evaluation of site effects at ridges characterized by complex geological setting

Abstract

The paper presents the results of site effects investigation at two villages, Castelvecchio Subequo and Castel di Ieri (Central Italy), located about 2 km from each other, on top of carbonate ridges characterized by complex geological/structural characteristics. Both villages suffered of an anomalous high damage degree determined by the Mw = 6.1, 2009 L'Aquila earthquake, highlighting the occurrence of significant ground motion amplification phenomena. Studying seismic response at rock sites characterized by complex geological setting is a challenging issue, as different factors can alter the expected ground motion. The difficulties arise from both the reconstruction of a suitable and thorough geological/geotechnical subsoil model and limitations of geophysical and numerical methods in such contexts. In order to overcome these difficulties, we here proposed an approach which integrates numerical modelling, based on the definition of a subsoil setting built from an accurate geological field analysis, with active and passive geophysical techniques. In particular, the calibration of numerical models based on transfer functions computed from Standard Spectral Ratio applied to noise recordings provided encouraging results.

Site response analyses for complex geological and morphological conditions: relevant case-histories from 3rd level seismic microzonation in Central Italy

“…At P2, 1D and 2D results are much closer; however, an evident 2D/1D peak of about 2 appears at 0.5s, substantially matching the H/V peak (about 2-2.5 Hz, Figure 7). The use of H/V shows therefore encouraging results in capturing also complex 2D effects as shown by other literature studies (Pagliaroli et al, 2015). Finally, it should be noted that the amount of amplification predicted by the numerical model satisfactorily matches the amplification estimated by the Generalized Inversion Technique (GIT) applied to several recordings carried out with a temporary network installed by the OGS institute after the August 24, 2016 event (Priolo et al 2019, this issue).…”

“…The Arquata case has shown the coupling between topographic effects and stratigraphic effects associated with the presence of an upper weathered/jointed portion of the rockmass ("atypical topographic effects" according to Massa et al 2014). In these contexts, the evaluation of site amplification is problematic (Pagliaroli et al, 2015). On the one hand, numerical codes do not generally allow a reliable representation of the subsoil complexity (e.g., discontinuous behavior of rock mass due to jointing); on the other hand, such materials are generally difficult or expensive to characterize with standard active geophysical techniques (i.e.…”

Active faulting, 3-D geological architecture and Plio-Quaternary structural evolution of extensional basins in the central Apennine chain, Italy

“…In general, at the edges of the basin, frequencies were between 1 and 5 Hz, with the exception of the area in front of Castelvecchio Subequo, where a series of NHVSR curves were flat, indicating the presence of bedrock close to the ground surface (Fig. S1, Table S1; see Marzorati et al, 2011, andPagliaroli et al, 2015, for details on the local seismic response in the Castelvecchio Subequo and Castel di Ieri areas). This is in agreement with the above-described geological observations.…”

Evaluation of complex site effects through experimental methods and numerical modelling: The case history of Arquata del Tronto, central Italy

“…The evaluation of local seismic response at sites characterized by complex geological and morphological features represents a crucial challenge. Difficulties mainly arise from both the reconstruction of a suitable and robust geological/geotechnical subsoil model and from limitations of geophysical and continuous numerical methods in such contexts (Pagliaroli et al, 2015).…”