Relationship Between Neotectonics And Fluid Escaping In The Northern Sicilian Continental Margin

New exploration in the marine environments has revealed that the fluid escape structures are often associated with neotectonic elements and are aligned along the same direction. Sometimes is observed the migration of fluid along fault planes to the sea floor as gas venting (Forrest et al., 2005). This paper aims to recognize and to classify the different types of structures associated with fluid seepage, particularly those that develop along alignments coinciding with or parallel to the neotectonic lineaments, in order to assess the interactions between tectonics and fluid circulation. The study area extends, from west to east, from the Gulf of Castellammare to the Gulf of Termini (offshore northern Sicily), and belongs to the northern Sicily continental margin, in the transitional area between the Sicilian-Maghrebian Chain to the south and the southern Tyrrhenian Sea to the north. Previous morphostructural studies identified a wide W–E trending right-lateral shear zone, mainly characterized by both a synthetic NW-SE/W–E trending, and antithetic left-lateral N–S/NE-SW fault systems, which affected the tectonic edifice, since the Pliocene (Giunta et al., 2009), while the current seismicity shows compressional focal mechanisms aligned to the NW-SE and ENE-WSW trends, in agreement with axis of maximum horizontal compression oriented NW-SE (Neri et al., 2003). We used a dataset of seismic reflection profiles, both high and very high resolution single-channel and multi-channel profiles, acquired respectively with CHIRP, sparker and airgun sources, and high resolution morphobathymetric data acquired down to 2200 m, in relation to the MaGIC project (Marine Geohazards along the Italian Coasts). The data allowed us to distinguish three different types of fluid escape structures by means of highly contrasting seismic and morphologic signatures. In particular, mounds and buried mounds have been recognized in the continental shelf, while pockmarks occur in the continental slope; the latter are often found to be aligned in this area. Two fault systems have been recognized: a NW-SE trending extensional and/or transtensional system, which produces the recent articulation of the seabed, and an ENE-WSW trending compressive, which contributed to the formation of morphological relieves. The seismicity of the area confirms the recent activity of both the systems, because the clusters of earthquakes of 1998, 2002 and the most recent until 2011 (http://www.ingv.it), are aligned with the recognized tectonic structures, and have focal mechanisms with major compression horizontal axis oriented NW-SE, compatible with the orientation of the tectonic lineaments. The identification of fluid escape structures, aligned with the neotectonic lineaments and with the clusters of earthquakes, allows us to hypothesize the relationship between the circulation of fluids and faults, the latter being preferential pathways for the rapid ascent of the fluid towards the surface. Moreover, the recent seismic activity indicates that the recognized neotectonic structures, respectively oriented NW-SE and ENE-WSW, are active and especially seismogenic structures.