Postseismic deformation following the 1997 Umbria-Marche (Italy) moderate normal faulting earthquakes

Abstract

We combine aftershock strain mapping, GPS measurements and leveling profiles with forward modeling of viscoelastic relaxation to study the postseismic deformation of the 1997 Umbria-Marche (Central Apennines) earthquake sequence. We explore the feasibility of GPS monitoring of postseismic transients, for the first time in Italy, generated by shallow and moderate sources. Our data allow us to distinguish a preferred coseismic faulting model as well as insight into the rheology of the Central Apennines Earth’s crust. The faulting model requires a listric geometry with most of the energy released in the lower half part of the elastic crust. The rheological model consists of an elastic thin upper crust, a transition zone of about 10 18 Pa s underlain by a low-viscosity lower crust, ranging from 10 17 to 10 18 Pa s. The postseismic deformation is, both distributed in the transition zone - lower crust and confined to the fault zone.