Understanding Holocene fault slip-rates along the Casamicciola Terme graben, Ischia, Italy

We conducted new UAV Lidar mapping, geomorphic, stratigraphic, and structural analyses along the 2 km long, E-trending, Casamicciola Terme Holocene graben, which follow the base of the 800 m high Mt Epomeo range front, in the N part of the Ischia Island, and is regarded as the source of the local damaging seismicity. We used UAV Lidar DEM at 10 cm resolution in order to map the graben capable normal faults and the sequence of the displaced marine terraces preserved in their footwall and hangingwall. This allow us to identify in detail the primary surface ruptures accompanying the August 21, 2017, Md 4.0 and July 28, 1883, Mw 5.2, earthquakes. We defined a new stratigraphic model of the graben area based on 25 available drilling data calibrated with 2 new stratigraphic boreholes at Piazza Maio and Grande Sentinella sites. Our new data, and comparison with available radiocarbon dating of the marine terraces along the N coast of Casamicciola and Lacco Ameno, and Ar/Ar dating of the Fundera lava flows, allow to constrain Holocene slip-rates for the synthetic and antithetic faults bounding the epicentral area of the strong 2017, 1883, 1881 and 1828 earthquakes. The S dipping fault at the S border of the Gran Sentinella terrace shows a slip-rate of ca. 6 mm/yr during the Late Holocene. The two parallel synthetic faults at the N-border of the Mt Epomeo slope show a cumulative slip rate of 26 mm/yr. The E-trending, N-dipping faults between Piazza Maio and the Montecito fumaroles represent one of several splays of the master fault responsible for the Holocene uplift of Mt Epomeo; which in turn is the source fault of the strong earthquakes occurred historically in the Casamicciola Terme and Lacco Ameno sector of the Ischia Island.