Coseismic and initial post-seismic slip of the 2009M_w6.3 L’Aquila earthquake, Italy, from GPS measurements

Abstract

S U M M A R YHere we report the preliminary results of GPS data inversions for coseismic and initial afterslip distributions of the M w 6.3 2009 April 6 L'Aquila earthquake. Coseismic displacements of continuous and survey-style GPS sites, show that the earthquake ruptured a planar SW-dipping normal fault with ∼0.6 m average slip and an estimated moment of 3.9 × 10 18 Nm. Geodetic data agree with the seismological and geological information pointing out the Paganica fault, as the causative structure of the main shock. The position of the hypocentre relative to the coseismic slip distribution supports the seismological evidence of southeastward rupture directivity. These results also point out that the main coseismic asperity probably ended downdip of the Paganica village at a depth of few kilometres in agreement with the small (1-10 cm) observed surface breaks. Time-dependent post-seismic displacements have been modelled with an exponential function. The average value of the estimated characteristic times for near-field sites in the hanging-wall of the fault is 23.9 ± 5.4 d. The comparison between coseismic slip and post-seismic displacements for the first 60 d after the main shock, shows that afterslip occurred at the edges of the main coseismic asperity with a maximum estimated slip of ∼25 cm and an equivalent seismic moment of 6.5 × 10 17 Nm. The activation of the Paganica fault, spatially intermediate between the previously recognized main active fault systems, suggests that strain accumulation in the central Apennines may be simultaneously active on distinct parallel fault systems.

On the complexity of surface ruptures during normal faulting earthquakes: excerpts from the 6 April 2009 L'Aquila (central Italy) earthquake (<i>M</i><sub>w</sub> 6.3)

“…4). All published coseismic slip models agree that most coseismic slip -up to 1.0 m -occurred between 9-10 and 3-4 km in depth, whereas slip in the shallowest crust was found to be 0.1 m or less over most of the fault length (e.g., Atzori et al, 2009;Cirella et al, 2009;Cheloni et al, 2010;D'Agostino et al, 2012;Cheloni et al, 2014). Shallower slip was documented mainly near the northern end of the fault (D'Agostino et al, 2012), about 3 km to the northeast of L'Aquila (Fig.…”

Spectral-Element Simulations of Seismic Waves Generated by the 2009 L'Aquila Earthquake

“…Imaging of the source (Anzidei et al, 2009;Atzori et al, 2009;Cirella et al, , 2012Pino and Di Luccio, 2009;Cheloni et al, 2010;Scognamiglio et al, 2010) highlights a complex rupture history composed of two main slip releases and controlled by spatial variations of material properties along the fault Lucente et al, 2010;Di Stefano, Chiarabba, et al, 2011) as well as temporal variations (Lucente et al, 2010;Zaccarelli et al, 2011). The source characteristics are partly responsible for the southeast directivity (Pino and Di Luccio, 2009;Akinci et al, 2010) and the unusually high levels of strong acceleration recorded close to L'Aquila city Çelebi et al, 2010).…”

The anatomy of the 2009 L'Aquila normal fault system (central Italy) imaged by high resolution foreshock and aftershock locations

“…Further details on fault geometry and slip distribution were derived from the modeling of Global Position System (GPS), synthetic aperture radar (SAR) data [Walters et al, 2009;Atzori et al, 2009;Anzidei et al, 2009;Cheloni et al, 2010;Lanari et al, 2010] and by the joint inversion of strong motion and geodetic data [Cirella et al, 2009].…”

“…These features have been interpreted as a direct expression of fault rupture. 3D laser scan technology (TLS) and GPS data located postseismic deformation around the main slip patches [Wilkinson et al, 2010;Cheloni et al, 2010]. [8] There are still open questions concerning the role played by the preexisting compressional structures on the evolution and geometry of Quaternary complex normal fault system and consequently on the deformation style of the central Apennine.…”