Search Results (3)

On 20 May 2012, an M_w 5.8 earthquake, followed by an M_w 5.6 event nine days later, struck the Emilia-Romagna region in northern Italy, causing substantial damage and loss of life. Post-mainshock, several water-related phenomena were observed, such as changes in the groundwater levels in wells, the expulsion of sand–water mixtures, and widespread liquefaction evidence such as sand boils and water leaks from cracks. We analyzed the Earth’s surface displacement during and after the Emilia 2012 seismic sequence using synthetic aperture radar images from the COSMO-SkyMed satellite constellation. This analysis revealed post-seismic ground subsidence between the Sant’Agostino and Mirabello villages. Specifically, the displacement time series showed a slight initial uplift followed by rapid subsidence over approximately four to five months. This widespread ground displacement pattern likely stemmed from the extensive liquefaction of saturated sandy layers at depth. This phenomenon typically induces immediate post-seismic subsidence. However, the observed asymptotic subsidence, reaching about 2.1 cm, suggested a time-dependent process related to post-liquefaction consolidation. To test this hypothesis, we analytically estimated the consolidation subsidence resulting from earthquake-induced excess pore pressure dissipation in the layered soil deposits. The simulated subsidence matched the observed data, further validating the significant role of excess pore pressure dissipation induced by earthquake loading in post-seismic ground subsidence. Full article

The first step for learning any calculation code for seismic response analysis is an adequate understanding of how to properly set the boundary conditions and the properties of the soil model at the initial stage, i.e., before the shaking event. To pursue this aim, nine different computer codes suitable for seismic response analyses of soil profiles have been reviewed. An ideal twenty-meter soil column with visco-elastic linear behavior, subjected to a pulse-like input motion, has been reproduced with the different codes with the scope to practically show the differences and peculiarities of each of them. In the definition of the soil properties in the small-strain range, special attention has been devoted to the definition of the damping ratio, usually defined in non-linear codes as viscous damping according to the Rayleigh formulation. This simple one-dimensional exercise has been considered as a useful benchmark for verifying the rightness of the application of the boundary conditions and setting the initial soil properties. The same analysis can be easily reproduced by beginner users and, therefore, constitutes a starting point in the learning phase of new and/or more sophisticated 2D and 3D calculation codes for seismic site response analysis. Full article

Many of the urban settlements in Central Italy are placed nearby active faults and, consequently, the ground motion evaluation and seismic site effects under near-fault earthquakes are noteworthy issues to be investigated. This paper presents the results of site investigations, the seismic site characterization, and the local seismic response for assessing the effects induced by the Mw 6.7 2 February 1703, near-fault earthquake at the Madonna delle Fornaci site (Pizzoli, Central Italy) in which notable ground failure phenomena were observed, as witnessed by several coeval sources. Even though recent papers described these phenomena, the geological characteristics of the site and the failure mechanism have never been assessed through in-situ investigations and numerical modeling. Within a project concerning the assessment of soil liquefaction potential and co-seismic ground failure, deep and shallow continuous core drilling, geophysical investigations and in-hole tests have been carried out. Subsequently, the geotechnical model has been defined and the numerical quantification of the different hypotheses of failure mechanisms has been evaluated. Analyses showed that liquefaction did not occur, and the excess pore water pressure induced by the shaking was not the source of the ground failure. Therefore, it was hypothesized that the sinkhole was likely caused by earthquake-induced gas eruption. Full article