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

Abstract

In May-June 2012, a seismic sequence struck a broad area of the Emilia-Romagna region in Northern Italy. The sequence included two mainshocks (on 20th May a ML 5.9 and on 29th May a ML 5.8). The whole aftershocks area extended in an E-W direction for more than 50 km, and included five ML ≥5.0 and more than 1,800 ML >1.5 earthquakes. Instrumental and historical local seismic records show low seismicity rate, the closest and more relevant historical earthquake being the 1570 A.D. earthquake that hit Ferrara. Widespread secondary geological effects were produced by the 2012 Emilia sequence and are mainly related to liquefaction phenomena. A total of more than 1,300 geologic coseismic effects were identified over more than 1,200 km 2 . We present some preliminary results concerning the study of the liquefactions occurred during the 2012 Emilia seismic sequence with particular emphasis on: (a) the definition of the areas most prone to liquefaction, (b) the identification and characterization of potential paleoliquefaction events. To identify the zones with high, medium or low liquefaction hazard, we show our quantitative approach defined to obtain a GIS based detailed analysis of the geometric relationships between the observed liquefactions and some peculiar geomorphic features of the 2012 epicentral. Differently, for recognition and characterization of paleoliquefaction events we adopted a multidisciplinary approach involving sedimentology, mineralogy and magnetic properties of the 2012 liquefied sands together with geophysical profiling, coring and dating.

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

“…In doing this, we took advantage of the huge amount of data on coseismic liquefaction effects related to the 2012 Emilia seismic sequence. Moreover, we put special emphasis on the fluvial features, already recognized as a potential control factor for the preferential location of liquefaction phenomena (Bertolini and Fioroni, 2012;Di Manna et al, 2012;EMERGEO Working Group, 2013;De Martini et al, 2014). Ridges, crevasse splays and riverbeds are usually richer in water-saturated coarse layers with respect to the whole flat alluvial plain (dominated by overflooding unsaturated fine deposits), and Fig.…”

“…It was already qualitatively noticed that the presence of subtle fluvial landforms in the area hit by the 2012 seismic sequence strongly influenced and favored the occurrence of liquefactions (Bertolini and Fioroni, 2012;Di Manna et al, 2012;Ninfo et al, 2012;De Martini et al, 2014;EMER-GEO Working Group, 2013;. In fact, looking at the distribution of the liquefaction features, it appears clearly that they are not evenly distributed over the area but are mostly arranged in clusters and rectilinear or meander-like alignments (Fig.…”

“…In more detail, the uppermost tens of meters of subsoil is composed by clay, silt and sand deposits organized in layers and lenses, related to the frequent migration of the rivers in the alluvial plain (Regione Emilia-Romagna, 1999;De Martini et al, 2014). Predominantly sandy and silty-sand deposits are generally found in coincidence with river channels, levees and crevasse splays, whereas all the areas dominated by clayey or silty-clayey deposits are related to lowenergy environments quite often "trapped" between active or paleo-riverbeds.…”

A comparison between bivariate and multivariate methods to assess susceptibility to liquefaction-related coseismic surface effects in the Po Plain (Northern Italy)

“…The subsoil lithology, down to a depth of about 20-30 m, is characterized by poorly consolidated fluvial deposits dated from the Upper Pleistocene to the Holocene. More in detail, the uppermost tens of meters are essentially constituted by sandy and silty-sand deposits, which are spatially related with river channels, levees and crevasse splays, representing the paleo-drainage patterns over the floodplain (De Martini et al 2015;Civico et al 2015). Data from ARPA Emilia Romagna (i.e.…”

When the earth blisters: Exploring recurrent liquefaction features in the coastal system of Christchurch, New Zealand

“…For several decades, alluvial, deltaic and coastal dune systems have been recognised worldwide as liquefaction‐prone settings (Alfaro, Estevez, Moretti, & Soria, ; Amick et al., ; Holzer, Noce, & Bennett, ; Moretti, ; Moretti, Pieri, & Tropeano, ; Tinsley et al., ; Tuttle, ; Youd & Hoose, ; Youd & Perkins, ). The CES studies (Almond et al., , ; Bastin, Quigley, & Bassett, ; Quigley, Bastin, & Bradley, ; Tuttle et al., in prep; Villamor et al., , ), together with studies from other recent liquefaction events (Alessio et al., ; Civico et al., ; De Martini et al., ; Fontana, Lugli, Marchetti Dori, Caputo, & Stefani, ), have focussed on the alluvial setting. Liquefaction features in the coastal setting of the Canterbury Plains have not been the subject of detailed study.…”