The Casamicciola fault system (Ischia Island, Campania region, Italy): mapping the surface trace of the 1883 and 2017 earthquake source from UAV LiDAR images and 2-D ERT profiles

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We present a high-resolution topographic map at 1:5000 scale of the northern slope of Mt Epomeo (Ischia Island, Italy), where the active Casamicciola fault system is exposed, and where coseismic surface ruptures associated with the 21 August 2017 earthquake (Md 4.0) were documented. This fault system is also considered the likely source of the destructive 28 July 1883 earthquake (Io = XI MCS), which caused extensive damage and approximately 2300 fatalities. The fault mapping was conducted by integrating UAV-based LiDAR-derived topography with extensive field investigations, 2-D Deep Electrical Resistivity Tomography, and seismic ambient noise measurements. Despite logistical challenges due to urban density, vegetation cover, and rugged terrain, fault scarps were identified and mapped in detail within the Casamicciola Holocene Graben. The map reveals a nested graben structure defined by two principal faults (Monte Cito and Sentinella) and two subsidiary ones (Purgatorio and Nizzola). Improved understanding of fault geometry is essential for seismic source characterisation and surface faulting hazard assessment in this densely populated, high-tourism region.