Do moderate magnitude earthquakes generate seismically induced ground effects? The case study of the M (w)=5.16, 29th December 2013 Matese earthquake (southern Apennines, Italy)

Seismically induced ground effects characterize moderate to high magnitude seismic events, whereas they are not so common during seismic sequences of low to moderate magnitude. A low to moderate magnitude seismic sequence with a M (w) = 5.16 +/- 0.07 main event occurred from December 2013 to February 2014 in the Matese ridge area, in the southern Apennines mountain chain. In the epicentral area of the M (w) = 5.16 main event, which happened on December 29th 2013 in the southeastern part of the Matese ridge, field surveys combined with information from local people and reports allowed the recognition of several earthquake-induced ground effects. Such ground effects include landslides, hydrological variations in local springs, gas flux, and a flame that was observed around the main shock epicentre. A coseismic rupture was identified in the SW fault scarp of a small-sized intermontane basin (Mt. Airola basin). To detect the nature of the coseismic rupture, detail scale geological and geomorphological investigations, combined with geoelectrical and soil gas prospections, were carried out. Such a multidisciplinary study, besides allowing reconstruction of the surface and subsurface architecture of the Mt. Airola basin, and suggesting the occurrence of an active fault at the SW boundary of such basin, points to the gravitational nature of the coseismic ground rupture. Based on typology and spatial distribution of the ground effects, an intensity I = VII-VIII is estimated for the M (w) = 5.16 earthquake according to the ESI-07 scale, which affected an area of at least 90 km(2).