Preliminary data and field observations of the 21st August 2017 Ischia earthquake

On 21st August 2017, an earthquake ($M_{L}3.6$; $M_{W}3.9$; $M_{d}4.0$) struck the municipality of Casamicciola Terme on the island of Ischia, Italy. It was a peculiar earthquake: low magnitude, very superficial (focus depth of about 1.7 km), centered in a high population density area. Despite the island was historically struck by destructive earthquakes during the last centuries, buildings vulnerability in the area was high. Many masonry buildings (main structural typology in Casamicciola Terme and on the island) collapsed or were severely damaged, occasionally exposing the original, dating back to end of nineteenth century, wooden frame that is one of the first examples of code designed anti-seismic structures in Italy. In this study, preliminary data and field observations of the 21st August 2017 Ischia earthquake are given. First, data from the permanent seismic network are used to assess seismic input characteristics and compare them to the known seismic hazard. Building vulnerability is then analyzed via the results of field observations carried out soon after the seismic event, thus providing significant information about quality of materials, construction techniques, structural performance and interpretation of possible damage mechanisms.