High‐resolution seismic imaging of the Mw5.7, 2002 Molise, southern Italy, earthquake area: Evidence of deep fault reactivation

Abstract

We investigate the seismic structure of the Mw5.7, 2002 Molise earthquake area in order to understand the role of E–W trending strike‐slip faults in the tectonics of the southern Apennines. We apply an innovative seismic migration technique to a high quality data set of earthquakes recorded at a dense local network. SP‐converted waves are migrated in depth to image the high impedance contrast of the Apulian Platform top buried under the Apennines allochthonous cover. The continuity of the migrated seismic horizon is broken by vertical steps that we systematically picked along 200 cross sections. The best location points of these structures define two main tectonic features. The first one is related to NW–SE oriented normal faults and is consistent with the SW flexure of the foreland lithosphere beneath the orogenic belt. The second one indicates that shallow E–Woriented trans‐tensional faults are concentrated directly above the deeper (10– 20 km) strike‐slip fault, delineating the geometry of a negative flower‐type structure. This fault system delimits a depressed sector of the Apulian Platform, whose geometry is consistent with a pull‐apart basin inherited from a previous left‐lateral strike‐slip tectonic regime. The buried structure is analogous to those outcropping in the Apulian foreland and in the Adriatic offshore, to the east. This correlation brings new support to the hypothesis of a regional E–W trending shear zone cutting the Adria plate and suggests that other earthquakes could occur on this or on parallel E–W trending strike‐slip faults.