Evidence of active tectonics in the Augusta Basin (eastern Sicily, Italy) by Chirp sub-bottom sonar investigation

Abstract

A Chirp sub-bottom sonar investigation was performed in the 150 km2 wide Augusta Basin, located offshore eastern Sicily, a region repeatedly hit by strong earthquakes in historical time, with the end of identifying possible evidence of active tectonics. Seismostratigraphy shows two main reflectors: R1, which represents the Last Glacial Maximum erosional surface, formed between 60 ka and 19 ka BP, and R2 that is the top of the Holocene deposits. Morphobathymetry reveals two marine abrasion surfaces, Ms1 and Ms2 that are related to the 35 ka and 25 ka BP marine high stills, respectively. R1 surface and the onlapping Holocene sediments are affected by normal and probably strike-slip faulting. The oldest NE-SW striking normal fault system dislocates R1 surface but not the Holocene deposit. NNW-SSE striking extensional faults show more recent activity since they displace Ms2 abrasion surface, the Holocene sequence and cause seafloor up-warping. NE-SW normal faults produce asymmetric basins where the Holocene deposits form wedged bodies. ENE-WSW left-lateral faults dissect a paleo-island, Ms2 and the NNW-SSE fault system. Moreover, seismically induced slumps involving the Holocene sediments, are found at the foot of some fault scarps. The presence of slumped bodies and active faults indicates ongoing deformation in the basin. Identified active faults are consistent with the main regional Malta Escarpment fault system, of which they can be considered as the incipient westernmost extension. This study supports the hypothesis that the Malta Escarpment is active and can be responsible for the regional seismicity. © 2013 by the Istituto Nazionale di Geofisica e Vulcanologia. All rights reserved.