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

Abstract

Abstract. The deformation pattern of the 6 and 7 April 2009 MW=6.3 and MW=5.6 earthquakes in L'Aquila is revealed by DInSAR analysis and compared with earthquake environmental effects. The DInSAR predicted fault surface ruptures coincide with localities where surface ruptures have been observed in the field, confirming that the ruptures observed near Paganica village are indeed primary. These ruptures are almost one order of magnitude lower than the ruptures that have been produced by other major surrounding faults in the past. These faults have not been activated during the 2009 event, but have the capacity to generate significantly stronger events. DInSAR analysis shows that 66% (or 305 km2) of the area deformed has been subsided whereas the remaining 34% (or 155 km2) has been uplifted. A footwall uplift versus hangingwall subsidence ratio of about 1/3 is extracted from the mainshock. The maximum subsidence (25 cm) was recorded about 4.5 km away from the primary surface ruptures and about 9 km away from the epicentre. In the immediate hangingwall, subsidence did not exceeded 15 cm, showing that the maximum subsidence is not recorded near the ruptured fault trace, but closer to the hangingwall centre. The deformation pattern is asymmetrical expanding significantly towards the southeast. A part of this asymmetry can be attributed to the contribution of the 7 April event in the deformation field.

Response to comments raised on “Surface deformation caused by April 6th 2009 earthquake in L’Aquila (Italy): A comparative analysis from ENVISAT ASAR, ALOS PALSAR and ASTER” by Chini Marco; Bignami Christian and Salvatore Stramondo

“…We demonstrated the subsidence in the LOS ranges from 25.1 cm to 28.1 cm from two ALOS PALSAR and two ENVISAT ASAR interferograms, respectively. The outcome of our work, are fully consistent with that of Walters et al (2009), GEER (2009) and Papanikolaou et al (2010. These references are also in agreement with the results achieved by Goudarzi et al (2011), that the greatest gradients are on the north-east area of the ENVISAT ASAR interferograms.…”

Quaternary coastline evolution of Lake Ohrid (Macedonia/Albania)

“…During movement along a normal fault, which means a downthrow of the hanging wall block, we observe, also, significant coseismic uplift within the footwall of the fault during an earthquake. The recent L'Aquila earthquake (6th April 2009) demonstrated that the ratio of the footwall uplift versus the hanging wall subsidence is around 0.3 [37]. Therefore, ongoing faulting and the de- velopment of listric normal faults has led to a tilted block, which partly separated a stretch of water, in a lagoon-like setting, from the lake.…”

Geometry of Holocene Tidal Notches – Sea Level Markers at Perachora Peninsula, Gulf of Corinth, Greece

“…Since tectonic uplift is a minor amount of coseismic displacements, vertical differences on a metre-scale between two notches are not reasonable for single and successive normal faulting earthquake events. More common are uplifting values in the order of a few decimetres (Papanikolaou et al, 2010). Hence, a mesoscale downward widening of pre-existing tidal notches is likely.…”

“…Stewart and Vita-Finzi, 1996;Armijo et al, 1996;McNeill et al, 2005;Papanikolaou et al, 2010). Pirazzoli et al (1994) identified a series of four tidal notches of Holocene age at Heraion (Figure 1), each displaced by repeated uplifts of about 0.8 ± 0.3 m. Assuming a ratio of ¼ net slip per event, this would equate to 4 m total offset in an area where Jackson et al (1982) reported just a minor coseismic uplift of 0.2 m during the Alkyonides earthquake sequence (M = 6.4-6.7) in spring 1981.…”