Distribution and Magnitude of Postseismic Deformation of the 2009 L’Aquila Earthquake (M6.3) Surface Rupture Measured Using Repeat Terrestrial Laser Scanning

We captured postseismic 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 days following the earthquake, we repeatedly laser scanned four road surfaces that intersected the earthquake surface rupture. We modeled vertical near-field deformation, at millimeter-level precision, by comparing subsequent laser scan datasets to the first acquired at each site. The horizontal postseismic 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 postseismic deformation between two points spanning the rupture. We find postseismic deformation increased between 44 – 126 days 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 postseismic deformation, within tens of meters 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 postseismic 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 postseismic deformation field.