Elusive active faults in a low strain rate region (Sicily, Italy): Hints from a multidisciplinary land-to-sea approach

Abstract

Low Strain Rate regions (LSRrs), i.e., areas undergoing tectonic deformation at rates of 1 mm/yr or less, often host important cities and highly vulnerable anthropogenic assets, and due to their subdued topography and relatively infrequent seismicity, are often considered low seismic hazard areas. Despite this, infrequent but high-magnitude earthquakes in such regions suggest that identifying active structures in the LSRr is one of the primary challenges for both the scientific community and modern societies. In such regions, one of the main issues in identifying active faults is the lack of valuable outcrop data due to erosional/sedimentation rates overwhelming the fault deformation, causing the hidden morphological signature of the tectonic structures. This work proposes a multidisciplinary approach designed to detect active geological structures and their related deformation in such areas. Our approach consists of quantitative morphotectonic, offshore and onshore tectonostratigraphic and GNSS joint analyses. To test this approach, we selected as a natural laboratory the partially offshore northern Sicilian LSRr (southern Italy) in the coastal sector located between the two major cities of Palermo and Termini Imerese. This area includes the compressional structures of the northern sector of the Apennine-Maghrebian fold and thrust belt, presently accommodating the slow Africa-Europe plate convergence. The main results we achieved are 1) new evidence of active tectonic deformation in this region; 2) the 3D modelling of two NNW-trending active faults; 3) the slip rate of a segment of the westernmost of the two detected faults; 4) a newly recorded relative GNSS velocity field; 5) a new morphotectonic map and morphotectonic evolution model of the study area. Our multidisciplinary approach allowed us to shed new light on the active tectonic framework of a slowly deforming area that crosses the physical limit of the coastline.