The 2009 L'Aquila (central Italy) M_W6.3 earthquake: Main shock and aftershocks

Abstract

Abruzzi region (central Italy) producing vast damage in the L'Aquila town and surroundings. In this paper we present the location and geometry of the fault system as obtained by the analysis of main shock and aftershocks recorded by permanent and temporary networks. The distribution of aftershocks, 712 selected events with M L ! 2.3 and 20 with M L ! 4.0, defines a complex, 40 km long, NW trending extensional structure. The main shock fault segment extends for 15-18 km and dips at 45°to the SW, between 10 and 2 km depth. The extent of aftershocks coincides with the surface trace of the Paganica fault, a poorly known normal fault that, after the event, has been quoted to accommodate the extension of the area. We observe a migration of seismicity to the north on an echelon fault that can rupture in future large earthquakes.

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

“…Therefore, the interferogram help us infer the influence of this smaller event to the deformation field. The 7 April event activated a zone SW from the mainshock, had a focal depth of approximately 15 km, but a rather unusual seismicity distribution so that its geometry is uncertain (Chiarabba et al, 2009;Pino and Di Luccio, 2009). No fault plane is distinguished by the aftershocks and moreover there is a large gap in the seismicity extending for almost 8 km (e.g.…”

“…This uplift feature can not be easily explained, but most probably is related to local unwrapping error. Another possibility could be if the 7 April M W =5.6 event was not SW dipping as the mainshock, but NE dipping since there are still large uncertainties regarding its geometry ( Chiarabba et al, 2009). For example, Pino and Di Luccio (2009) recognize a confused pattern about this event, but they promote a NE dipping solution.…”

“…This occurs not only because the Paganica ruptures correlate with well the focal mechanism and the epicenter locality (e.g. Chiarabba et al, 2009), but mainly due to the DInSAR analysis results (see also Atzori et al, 2009;Walters et al, 2009). In particular, the approximately 7 km long DIn-SAR predicted fault surface ruptures coincide with the surface ruptures observed in Paganica since they are only a couple of hundred meters up to 1 km apart (Fig.…”

“…Initially, the aftershock activity occurred near L'Aquila and towards the south-east of the town, whereas a couple of days later it migrated towards the NE at Barrete and Campotosto. The seismicity covers a rectangulary elongated area that is approximately 40 km long and 10-12 km wide trending towards the NW-SE (Chiarabba et al, 2009;Pondrelli et al, 2009). Roberts et al 2002).…”

Separation of source and site effects by generalized inversion technique using the aftershock recordings of the 2009 L’Aquila earthquake

“…After the 6 April L'Aquila mainshock (Chiarabba et al, 2009), 33 seismic stations (both accelerometers and velocimeters) were deployed in the Aterno river Valley in order to record the aftershocks and to characterize the seismic response of the area (see Cultrera et al, 2009 and Bergamaschi et al, this issue, for a detailed description of the experiment). The collected dataset includes the recordings from more than 100 earthquakes with magnitudes larger than 3 that occurred from April 7 th to May 15 th 2009 and were located within 30 km from the L'Aquila mainshock epicenter.…”