Liquefaction phenomena associated with the Emilia earthquake sequence of May–June 2012 (Northern Italy)

Abstract

Abstract. In this paper we present the geological effects induced by the 2012 Emilia seismic sequence in the Po Plain. Extensive liquefaction phenomena were observed over an area of ~ 1200 km2 following the 20 May, ML 5.9 and 29 May, ML 5.8 mainshocks; both occurred on about E–W trending, S dipping blind thrust faults. We collected the coseismic geological evidence through field and aerial surveys, reports from local people and Web-based survey. On the basis of their morphologic and structural characteristics, we grouped the 1362 effects surveyed into three main categories: liquefaction (485), fractures with liquefaction (768), and fractures (109). We show that the quite uneven distribution of liquefaction effects, which appear concentrated and aligned, is mostly controlled by the presence of paleo-riverbeds, out-flow channels and fans of the main rivers crossing the area; these terrains are characterised by the pervasive presence of sandy layers in the uppermost 5 m, a local feature that, along with the presence of a high water table, greatly favours liquefaction. We also find that the maximum distance of observed liquefaction from the earthquake epicentre is ~ 30 km, in agreement with the regional empirical relations available for the Italian Peninsula. Finally, we observe that the contour of the liquefaction observations has an elongated shape almost coinciding with the aftershock area, the InSAR deformation area, and the I ≥ 6 EMS area. This observation confirms the control of the earthquake source on the liquefaction distribution, and provides useful hints in the characterisation of the seismogenic source responsible for historical and pre-historical liquefactions.

Aftershocks, groundwater changes and postseismic ground displacements related to pore pressure gradients: Insights from the 2012 Emilia‐Romagna earthquake

“…The LOS displacement time series (point 3 in Figure 2c) show an initial slight postseismic uplift, which is followed by a rapid subsidence that asymptotically decreases over approximately 3 months. Such diffused pattern of ground displacements is ascribable to the widespread liquefaction phenomena observed in the area a few days after the main shock [Alessio et al, 2013] (white circles in Figure 2b). Such phenomena (i.e., sand boils and water leaks from cracks) generally produce ground settlements not only in the affected area but also where the liquefaction phenomena are not recognized [Chini et al, 2015].…”

“…The monitored wells close to the epicentral area registered a sudden increase in water level that was followed by a decay that did not reach the preseismic level during the observation period [Marcaccio and Martinelli, 2012]. Some wells ejected a mixture of water and sand, and more than 700 liquefaction phenomena were observed [Alessio et al, 2013;Chini et al, 2015]. Furthermore, a periodic sampling of both liquid and gaseous phases in surficial aquifers established that deep-seated fluids was mobilized after the main shock and reached surface layers along faults and fractures, thus altering the geochemical composition of fluids [Italiano et al, 2012;Sciarra et al, 2012].…”

Liquefaction susceptibility assessment in fluvial plains using airborne lidar: the case of the 2012 Emilia earthquake sequence area (Italy)

“…An area of approximately 1200 km 2 was covered by the 2012 post-earthquake surveys, and coseismic geological evidence was collected through field reconnaissance and aerial surveys, reports from local people and Web-based surveys (EMERGEO Working Group, 2012a, 2013. More than 1350 coseismic geological effects were identified at the surface (Fig.…”

“…The huge amount of data on coseismic liquefaction related to the May-June 2012 events (EMERGEO Working Group, 2012a, 2013) offers a unique opportunity to refine our knowledge and methodologies to better understand how the geomorphological setting, besides the stratigraphic and hydrologic conditions, can favor the occurrence of liquefaction phenomena.…”

Geological and Geophysical Approaches for the Definition of the Areas Prone to Liquefaction and for the Identification and Characterization of Paloeliquefaction Phenomena, the Case of the 2012 Emilia Epicentral Area, Italy

“…The huge amount of data on coseismic liquefaction related to the May-June 2012 events (EMERGEO Working Group 2013;Fig. 184.1) offers a unique opportunity to refine our knowledge and methodologies to characterize the liquefaction phenomena.…”