Assessment of post-liquefaction consolidation settlements after the 2012 Emilia earthquake. Extended Summary, Oral presentation.

An earthquake with a magnitude of 5.8 struck the Emilia-Romagna region in northern Italy on 20 May 2012, resulting in significant damage and loss of life. In the days following the main shock, the rupture spread eastward and downward along the Ferrara thrust system, and westward along the neighbouringMirandola thrust, leading to another earthquake of magnitude 5.6 on 29 May. After the initial earthquake, a number of postseismic events occurred. Wells in the vicinity of the epicentre experienced a sudden rise in water levels, followed by a gradual decline that did not return to preseismic levels within the observation period. Some wells even expelled a mixture of water and sand, and over 700 instances of liquefaction were observed. We conducted a study on the displacement of the Earth's surface during and after the Emilia 2012 seismic sequence, using a dataset comprising 18 synthetic aperture radar (SAR) images obtained from the descending orbit of COSMO-SkyMed (CSK) constellation satellites. Analysis of the SAR data over time revealed that the area between S. Agostino and Mirabello villages underwent postseismic ground subsidence. Specifically, the displacement time series in the region displayed a slight initial uplift, followed by a rapid subsidence that gradually decreased over a period of approximately three months. This widespread pattern of ground displacement can be attributed to the extensive liquefaction phenomena observed a few days after the main earthquake. These phenomena, such as the emergence of sand boils and water leaks from cracks, typically result in immediate ground settlements following a seismic event. However, the delayed attainment of asymptotic settlement after approximately three months suggests a process of post-liquefaction consolidation. To test this hypothesis, we employed an analytical method to estimate the consolidation settlement caused by the dissipation of excess pore pressure induced by the earthquake. The simulated settlements align with the observed data both spatially and temporally. This provides further validation to the hypothesis that the dissipation of excess pore pressure induced by the earthquake loading played a significant role in the postseismic ground subsidence.