Seismic constraints on the present-day kinematics of the Gargano foreland, Italy, at the transition zone between the southern and northern Apennine belts

The 1995-2004 seismicity in the Gargano Promontory (hereafter GP) foreland at the transition zone between Southern and Northern Apennine belts (Italy) is analyzed with the aim to put constraints on the present-day kinematics of this key-area of the foreland. The spatial distribution of earthquakes and 54 calculated focal mechanisms show that that the main GP ruptures develop along E-W striking, right-lateral strike-slip faults and NW-SE, normal to left-lateral second-order faults that move in response to a prevailing NW-SE compression (i.e. NE-SW extension). Tacking into account the depth of the relocated seismicity and the available geological information, we propose that the GP shear zone represents an E-W striking, major crustal discontinuity separating sectors of the foreland that move in response to the higher, northeastward propagation velocity of the thrust front of the Northern Apennines with respect to that of the Southern Apennines.