Exploring the resurgence stage of Ischia caldera by coupling 2D numerical modelling and high-resolution remote sensing

Ischia Island, Italy, is a densely populated, active resurgent volcanic caldera that has undergone rapid deformation during the Holocene. The northern sector of the island, particularly the Casamicciola area, is notable for destructive shallow earthquakes, among the most severe in the Italian seismic catalog; for instance, the 1883 event claimed more than 2300 lives.

Dense vegetation has historically hindered detailed mapping efforts, but the application of drone-based LiDAR has facilitated us a high-resolution neotectonic mapping. Previously, we investigated the fault geometries along the Casamicciola Holocene Graben fault by integrating high-resolution remote sensing data with field-based mapping techniques in the epicentral area of the 1883, Mw 5.0, and 2017, Md 4.0, earthquakes.

The identified fault structures served as initial conditions for numerical simulations using the mantle convection and lithospheric dynamics code ASPECT. The simulations incorporated the effects of fault strength variations, high geothermal gradients, and contrasts in viscosity and mechanical properties on Holocene deformation distribution. Three primary scenarios were tested: (1) deformation driven by regional NE-SW extensional tectonic stress, (2) deformation caused by pressurization of a magmatic intrusion driving resurgence, and (3) deformation resulting from magma depressurization associated with subsidence.

Results reveal that the high deformation rates are primarily driven by shallow magmatic intrusions (~2 km depth) that induce resurgence of the caldera floor, with minimal contribution from regional tectonic stress. Modelled cumulative slip rates during the Holocene, range from 5.0 mm/yr to 31.12 mm/yr, closely matching rates derived from geological data. Additionally, velocity profiles simulating magma intrusion elucidate how the geometry, pressure, and volume of magma govern the asymmetric uplift of the caldera floor. These findings provide insights into the relationship between magmatic processes and earthquake occurrences in the Casamicciola Holocene Graben.