Rupture history of the 2009 L'Aquila (Italy) earthquake from non‐linear joint inversion of strong motion and GPS data

Abstract

We image the rupture history of the 2009 L'Aquila (central Italy) earthquake using a nonlinear joint inversion of strong motion and GPS data. This earthquake ruptured a normal fault striking along the Apennines axis and dipping to the SW. The inferred slip distribution is heterogeneous and characterized by a small, shallow slip patch located up‐dip from the hypocenter (9.5 km depth) and a large, deeper patch located southeastward. The rupture velocity is larger in the up‐dip than in the along‐strike direction. This difference can be partially accounted by the crustal structure, which is characterized by a high velocity layer above the hypocenter and a lower velocity below. The latter velocity seems to have affected the along strike propagation since the largest slip patch is located at depths between 9 and 14 km. The imaged slip distribution correlates well with the on‐fault aftershock pattern as well as with mapped surface breakages.

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.…”

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

“…Consistently the surface ruptures were observed only along the MSF and Paf segments (Figure 9). This aspect is also evident by plotting together the aftershocks of the L'Aquila fault, the mapped faults (MSF, PaF and SDF) and the coseismic slip proposed by Cirella et al [2009], along a downdip section containing the main shock (Figure 19).…”

“…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].…”

Deformation pattern of the 6 and 7 April 2009, <i>M</i><sub>W</sub>=6.3 and <i>M</i><sub>W</sub>=5.6 earthquakes in L'Aquila (Central Italy) revealed by ground and space based observations

“…The PGA values are stretched to the south east, indicating directivity effects in the rupture propagation (Ameri et al, 2009;Akinci et al, 2009). This strong directivity effect towards the SE revealed by the accelerometers, and the heterogeneous slip distribution (Cirella et al, 2009), favours an inherent asymmetry of the mainshock. One way to find out whether this SE prolongation of the deformation field can be attributed only to the 7 April or not, would be to extract the estimated deformation field of the 7 April event from the cumulative field and trace whether this asymmetry still remains or not.…”