Modelling the 3D complexities of a subduction interface: the Calabrian Arc (Italy)

Abstract

Geometric complexities of subduction interfaces can be crucial for seismic and tsunami hazard studies because they may reveal important elements for constraining the dimension of future potential ruptures and even the location of asperities. Here we present the results of a recent work focused on the subduction interface of the Calabrian Arc where a remnant of the oldest oceanic crust in the world (280 Myr) forms a very narrow slab (~150 km). Historical and instrumental earthquake catalogues show no events that can be unequivocally assigned to the Calabrian subduction interface, nonetheless a significant in-slab seismicity below 40 km depth and a convergence rate of 1-5 mm/yr between the two involved plates (Africa and Europe) warn about the current activity of the subduction system and its possible seismogenic behaviour. Our 3D reconstruction of the Calabrian subduction interface (figure 1) merges a shallow part (<20 km) based on the interpretation of ca. 9000 km of seismic reflection profiles (data provided by Spectrum Geo, collaborative framework with INGV CA-60), and a deeper part (20-350 km) reconstructed by analysing the seismicity distribution and the available tomographic data. The resulting model images several peculiar features that characterize the Calabrian subduction interface, such as an external shallow flat, a central ramp with lateral dip variations, and a deeper flat. The lateral terminations are characterized by the thrusting over the Apulian continental margin in the northern part and a Subduction Transform Edge Propagator fault system in the southern part. At 100-150 km depth the subduction is characterized by a slab breakoff. Geometric parameters that can be derived from the 3D model, such as the size and curvature of the interface, are often related to the seismogenic potential of subduction zones through empirical or model–driven scaling laws. In the case of the Calabrian subduction interface such fault scaling relations yield estimates of the maximum moment magnitude in the order of 8, if fully coupled.