L. Alfonsi

Coseismic ruptures of the 24 August 2016, Mw 6.0 Amatrice earthquake (central Italy)

On 24 August 2016, a Mw 6.0 normal faulting earthquake struck central Italy, causing about 300 fatalities and heavy damage. A geological survey collected the coseismic effects observed at the surface in order to evaluate two competing hypotheses about their nature: surface faulting versus gravitational deformation. We find that the most significant geological effect is a 5.2 km-long alignment of ground ruptures along the Mt. Vettore Fault-System. These ruptures are independent from lithology, topography, morphology and change in slope and exhibit an average dip slip displacement of ~13 cm. Geometry, kinematics and dimensional properties of this zone of deformation strongly lead us to favor the primary surface faulting hypothesis that fits well the predicted estimates from experimental scaling-law relationships. Our study provides relevant hints for surface faulting in extensional domains, contributing to implement the worldwide database of the moderate earthquakes.

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

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 km2. 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.