Strain accumulation in the southern Alps (NE Italy) and deformation at the northeastern boundary of Adria observed by CGPS measurements

Abstract

We use continuous GPS observations to investigate the rate of strain accumulation in the area affected by the 1976 Friuli earthquakes. Comparison between the motion predicted by the rigid-rotation of Adria and the shortening observed across the study area suggests that the 2.0 ± 0.2 mm/yr motion of Adria is entirely absorbed in the southern Alps through thrusting and crustal thickening with very little or no motion transferred to the north. We use elastic dislocation modelling to investigate the rate of interseismic loading and the geometry of the shear zone at depth. The best-fit solution indicates that a northward-dipping creeping dislocation, whose edge is located within a 50 km wide area beneath the southern Alps, accomodates 2.1 ± 0.5 mm/yr of the Adria motion. Limited resolution on locking depth (acceptable values between 0 and 25 km) and trade-off between dip and slip do not allow a precise reconstruction of the dislocation geometry. The range of acceptable model parameters is consistent with a 20°-dipping dislocation, locked above 10 km depth and slipping at 2.4 mm/yr, whose geometry is suggested by seismological informations. Copyright 2005 by the American Geophysical Union.