First evidence of post-seismic deformation in the central Mediterranean: Crustal viscoelastic relaxation in the area of the 1980 Irpinia earthquake (Southern Italy)

Comparison between measured vertical displacements obtained from two levelling campaigns performed in 1981 and 1985 in the epicentral area of the 1980 Irpinia earthquake (M-S = 6.9) and predictions from viscoelastic Earth models reveal the occurrence of post-seismic deformation due to stress relaxation in the ductile part of the crust. Two regions of broad uplift and subsidence, accumulated during the time interval, characterize the deformation pattern in the footwall and hangingwall of the major fault. The spatial wavelength of the deformation pattern favours relaxation occurring in the lower crust rather than in a weak upper-mantle: the uplift in the footwall explains the 30 mm of upwarping of the crust measured along the levelling line crossing the area where the fault pierces the Earth's surface.