Ground effects induced by the 2012 seismic sequence in Emilia: implications for seismic hazard assessment in the Po Plain

Abstract

<p>Since May 16, 2012, a seismic sequence has affected a wide portion of the Emilia Region (northern Italy), chiefly for the Modena and Ferrara Provinces. The first mainshock (Ml 5.9; focal depth, ca. 6 km) occurred on May 20, 2012, with the epicenter located a few kilometers north of Finale Emilia. A second main shock (Ml 5.8; focal depth, ca. 10 km) occurred on May 29, 2012, about 12 km west of the first earthquake, with the epicenter near Medolla (Figure 1). The seismic sequence has been characterized by five other Ml ≥5 events, and more than 2,300 aftershocks of lower magnitude, until the end July 2012. The distribution of the aftershocks identifies a WNW-ESE-trending zone ca. 40 km long that is characterized by NNE-SSW nearly pure compression, as indicated by the focal mechanisms [e.g., QRCMT 2012]. This report focuses on the many ground effects that were induced by this seismic sequence, as mainly cracks, liquefaction-type phenomena, and hydrological anomalies. The aim is to provide a complete representation of such effects, to: illustrate their type, size and areal distribution; identify the zones in the affected area that were most prone to the occurrence of ground effects (i.e., more susceptible to local geological instability in the case of earthquake occurrence); carry out an independent assessment of the intensities of the earthquakes through the ESI 2007 intensity scale [Guerrieri and Vittori 2007], which is based only on coseismic effects on the natural environment. […]</p>

Down-hole geophysical characterization of middle-upper Quaternary sequences in the Apennine Foredeep, Mirabello, Italy

“…The 2012 earthquakes triggered a widespread interest on the seismic hazard assessment in the alluvial plain area of the Emilia-Romagna Region [Di Manna et al 2012, Malagnini et al 2012, Meletti et al 2012, Milana et al 2014, Papathanassiou et al 2015, Tonni et al 2015]. The available data on the subsurface were however scanty.…”

Interplay of Holocene surface faulting and climate in the Central Po Plain, Italy

“…Widespread liquefaction phenomena occurred during the 2012 seismic sequence of Ferrara (Di Manna et al, 2012) in a comparable stratigraphic and sedimentological context, which can be considered as a natural laboratory to investigate surface structures related to liquefaction. This seismic sequence was characterized by two main events that occurred during May 2012 (20 May 2012 Mw 6.1 and 29 May 2012 Mw 5.9), with a hypocentral depth of 6.3 km and 10.2 km, respectively.…”

“…Considering the 2012 seismic sequence of Ferrara as a natural laboratory for directly testing parameters related to liquefaction, it was observed that liquefaction occurred only during the two main events (Di Manna et al, 2012). A maximum distance of 27 km from the epicenters was recorded for significant liquefaction, but no liquefaction occurred during the other events with a lower magnitude.…”

“…Liquefaction at Ferrara was particularly intensive along paleochannels due to favorable conditions related to grain size of the sediments (silt/fine-grained sand) combined with elevation of the groundwater level (Di Manna et al, 2012). Artificial trenching across the Reno River close to the town of Ferrara (Caputo et al, 2016) also revealed widespread liquefaction phenomena related to the 1570 AD seismic event that also affected the same area, attesting that this was a common indicator of past seismic shaking in the lowermost reaches of the Po Plain.…”

Congresso SIMP-SGI-SOGEI 2019 - Il tempo del pianeta Terra e il tempo dell'uomo: Le geoscienze fra passato e futuro

“…The ESI scale integrates the traditional macroseismic scales, of which it represents the evolution, allowing to assess the intensity parameter also where buildings are absent or damage-based diagnostics saturate. For this purpose, we revisit three representative case histories from very different tectonic environments: the reverse faulting of the 2012 Emilia sequence (May 20, M w = 5.8; and May 29, M w = 5.6; Di Manna et al, 2012) in the Po Plain foredeep environment of N Italy; the normal faulting of August 21, 2017 Casamicciola earthquake (M d = 4.0;Nappi et al, 2018) in the Ischia volcanic island, S Italy; and the devastating February 4, 1976, Guatemala earthquake (M = 7.5;Porfido et al, 2015), along the leftlateral Motagua Fault at the boundary between the N America and Caribbean plates.…”