The moderate earthquake occurred at the volcanic island of Ischia, south-west of Naples (Italy) caused several buildings collapse, two victims, and several tens of injured people. This event generated a large amplitude ground shaking and long-lasting S-wave signal, longer than those expected for an earthquake. To investigate the event rupture complexity and its radiated wave field, we used finite-fault modelling to invert the near-source (< 1 km epicentral distance), three-component velocity records of the accelerometric station (IOCA), and searched for the best-fit kinematic rupture parameters. This analysis showed that the rupture nucleated at about 600 m west of IOCA and 1.1 km depth, along a 1 km, NW-SE striking fault (thrust-strike slip with right-lateral component), with a rupture velocity 0.8 km/s. The retrieved rupture model coupled with multi-path reverberations effects related to a thin, low-velocity near-surface volcanic sedimentary layer, allowed us to explain the observed long ground motion duration and the large amplitudes recorded all over the island. The actual fault location, mechanism, and the spatial correlation between the simulated peak ground motion zone and the area where the maximum vertical displacement has been determined by DInsar images suggest that the latter is associated with strong-shaking locally generated by land-slide phenomena caused by co-seismic slip. Our source model is consistent with the earthquake located near the border of the caldera resurgent block, which is likely still active, where mass rock creeps evolved into widespread collapses at NW of Monte Epomeo.