Coseismic evidence of surface faulting at the Ischia Volcanic Island after the 21 August 2017 Md 4.0 Casamicciola Earthquake.

We provide a database of the coseismic surface ruptures produced by the 21 August 2017 Md 4.0 earthquake that struck the Casamicciola Terme village in the north of Ischia volcanic island (Italy). Despite its small size, the earthquake caused two fatalities and heavy damages in a restricted area of a few square kilometers. The shallow hypocentral depth of the earthquake caused a significant coseismic surface faulting, testified by a main alignment of ruptures mapped for a 2 km end-to-end length along the Casamicciola E-W trending normal fault system, bounding the northern slope of Mt. Epomeo. Casamicciola Terme has been recurrently destroyed in the last centuries by similar volcano-tectonic earthquakes (1762, 1767, 1796, 1828, 1881, and 1883). After the catastrophic 1883 Casamicciola event (2343 casualties), this is the first heavy damaging earthquake at Ischia that provides, for the first time, the opportunity of integrating historical seismicity, macroseismic observations, instrumental information, and detailed mapping of coseismic geological effects. We performed a detailed field surveys in the epicentral region of the 21 August earthquake to describe the ruptures geometry and kinematics of the seismogenetic fault responsible of the earthquake with the aim of contributing to the seismic hazard evaluation and land use planning in the Ischia island, one of the most crowded touristic destinations worldwide. Summarizing our study of ground effects for the 21 August 2017 earthquake is important for improving knowledge on surface earthquake in the volcanic area and contributing to complete the gap of empirical scaling relating to the surface-faulting mechanism due to small-size or moderate earthquakes in volcano-tectonic framework. The collected field observations result in a dataset of 88 georeferenced records describing coseismic ruptures/fractures by features as ID number, time of sample collection, location (latitude, longitude, elevation), type of rupture, type of affected substratum, attitude (dip angle, dip direction, strike), surface offset (opening, throw, strike slip, net slip), kinematics, slip vector attitude, width of the deformation zone.