Liquefaction phenomena along the paleo-Reno River caused by the May 20, 2012, Emilia (northern Italy) earthquake

Giorgos Papathanassiou Giorgos Papathanassiou,Riccardo Caputo Riccardo Caputo,Dimitra Rapti-Caputo Dimitra Rapti-Caputo

doi:10.4401/ag-6147

Giorgos Papathanassiou Giorgos Papathanassiou, Riccardo Caputo Riccardo Caputo + Show 1 more

Open Access

https://doi.org/10.4401/ag-6147

Copy DOI

Abstract

<p>On the May 20, 2012 (04:03:52 local time; 02:03:52 UTC), a moderate earthquake (Ml 5.9) [Scognamiglio et al. 2012, this volume] with a focal mechanism showing E-W-trending, S-dipping, reverse-faulting occurred in the eastern sector of the alluvial plain of the Po River, close to the border between the Regions of Emilia-Romagna and Lombardia (northern Italy). The tectonic structure is completely blind, but it was well known from a dense grid of seismic profiles for hydrocarbon explorations [e.g., Pieri and Groppi 1981, Toscani et al. 2009]. The earthquake triggered extensive liquefaction-induced ground effects at the surface, and caused severe structural damage to nonreinforced masonry and precast industrial buildings within the broader epicentral area. The hypocenter was at 44.89 ˚N, 11.23 ˚E, at a depth of 6.3 km [Scognamiglio et al. 2012], while the maximum acceleration was recorded in Mirandola, with peak ground acceleration 310 cm/s2 and 264 cm/s2 along the vertical and horizontal components, respectively [Bozzoni et al. 2012, this volume]. In this report, we focus on a zone including the Sant'A-gostino, San Carlo and Mirabello villages (west Ferrara Province), which were built along an abandoned reach of the Reno River and where liquefaction phenomena were particularly diffuse, with very intense local effects. […]</p>

Highlights

On the May 20, 2012 (04:03:52 local time; 02:03:52 UTC), a moderate earthquake (ML 5.9) [Scognamiglio et al 2012, this volume] with a focal mechanism showing E-W-trending, S-dipping, reverse-faulting occurred in the eastern sector of the alluvial plain of the Po River, close to the border between the Regions of Emilia-Romagna and Lombardia
The questions posed focused on the timing of the ejection phenomena, relative to the occurrence of the mainshock, the duration of the outflow, and the height of the ejection with respect to the ground surface. Important outcomes of these interviews were: (i) most of the sandy material within the three urban areas that was focused on (Mirabello, San Carlo, Sant'Agostino) was ejected through large diameter water wells; (ii) the ejection of sandy material started almost at the same time as the mainshock; and (iii) in the first seconds/minutes of the ejection process, clear water came to the surface first, only later mixed with sand
Taking into account the length and width of the surface ruptures, and the dimensions of vent fractures and sand boils of liquefaction phenomena, we conclude that the macroseismic intensity should be evaluated as VIII in the area of San Carlo

Summary

Introduction

On the May 20, 2012 (04:03:52 local time; 02:03:52 UTC), a moderate earthquake (ML 5.9) [Scognamiglio et al 2012, this volume] with a focal mechanism showing E-W-trending, S-dipping, reverse-faulting occurred in the eastern sector of the alluvial plain of the Po River, close to the border between the Regions of Emilia-Romagna and Lombardia (northern Italy). The length and width of vent fractures, and the diameter of the sand craters were measured, and samples were collected from ejected materials at representative sites.

Results

Conclusion