Distribution and magnitude of post-seismic deformation of the 2009 L’Aquila earthquake (M6.3) surface rupture measured using repeat terrestrial laser scanning

Abstract

We captured post-seismic deformation close to the surface rupture of the 2009 L’Aquila earthquake (M6.3, central Italy) using repeat terrestrial laser scan (TLS) methods. From 8 to 126 d after the earthquake, we repeatedly laser scanned four road surfaces that intersected the earthquake surface rupture. We modelled vertical near-field deformation, at millimetre-level precision, by comparing subsequent laser scan data sets to the first acquired at each site. The horizontal post-seismic deformation at each site was measured between reflectors paired across the rupture. The TLS data were supplemented by total station data from a fifth site which measured the vertical and horizontal components of post-seismic deformation between two points spanning the rupture. We find post-seismic deformation increased between 44 and 126 d at the southeastern end of the rupture, beneath which a significant gradient in coseismic slip exists within the fault zone. The location, rate of decay and spatially-localized nature of the post-seismic deformation, within tens of metres of the surface rupture suggests it is due to afterslip in the fault zone, driven by increased shear stresses at the edges of regions which slipped coseismically. We note that the magnitude of post-seismic deformation in the far field obtained from InSAR and GPS is not significantly greater than the deformations we have measured close to the rupture. We suggest that shallow, localized afterslip within the fault zone is responsible for the majority of the regional post-seismic deformation field.