The 2009 L'Aquila earthquake (central Italy): A source mechanism and implications for seismic hazard

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.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Deformation pattern of the 6 and 7 April 2009, MW=6.3 and MW=5.6 earthquakes in L'Aquila (Central Italy) revealed by ground and space based observations

Papanikolaou

Foumelis

Parcharidis

et al. 2010

“…Notice that various methods show that the top of the activated fault is located from 3.0 km up to 0 km bellow from the Earths surface (Walters et al, 2009). The observed anomalies followed this temporal scheme: Two MHz electric anomalies appeared on 26 March 2009 and 2 April 2009 (Fig.…”

Section: Em Anomalies Observed Prior To the L'aquila Earthquakementioning

confidence: 99%

Unfolding the procedure of characterizing recorded ultra low frequency, kHZ and MHz electromagnetic anomalies prior to the L'Aquila earthquake as pre-seismic ones - Part 2

Eftaxias¹,

Athanasopoulou²,

Balasis³

et al. 2010

147

Abstract. Ultra low frequency-ULF (1 Hz or lower), kHz and MHz electromagnetic (EM) anomalies were recorded prior to the L'Aquila catastrophic earthquake (EQ) that occurred on 6 April 2009. The detected anomalies followed this temporal scheme. The question effortlessly arises as to whether the observed anomalies before the L'Aquila EQ were seismogenic or not. The main goal of this work is to provide some insight into this issue. More precisely, the main aims of this contribution are threefold: How can we recognize an EM observation as pre-seismic one? We aim, through a multidisciplinary analysis to provide some elements of a definition. How can we link an individual EM anomaly with a distinctive stage of the EQ preparation process? The present analysis is consistent with the hypothesis that the kHz EM anomalies were associated with the fracture of asperities that were distributed along the L'Aquila fault sustaining the system, while the MHz EM anomalies could be triggered by fractures in the highly disordered system that surrounded the backbone of asperities of the activated fault. How can we identify precursory symptoms in an individual EM precursor that indicate that the occurrence of the EQ is unavoidable? We clearly state that the detection of a MHz EM precursor does not mean that the occurrence of EQ is unavoidable; the Correspondence to: K. Eftaxias (ceftax@phys.uoa.gr) abrupt emergence of kHz EM emissions indicate the fracture of asperities. The observed ULF EM anomaly supports the hypothesis of a relationship between processes produced by increasing tectonic stresses in the Earth's crust and attendant EM interactions between the crust and ionosphere. We emphasize that we attempt to specify not only whether or not a single EM anomaly is pre-seismic in itself, but mainly whether a combination of emergent ULF, MHz and kHz EM anomalies could be characterized as pre-earthquake.

“…The strong (M w = 6.3) earthquake of 6 April 2009 in L'Aquila, Central Italy, occurred at 01:32:39 UTC and caused about 300 deaths and destruction in about 60 000 buildings of the area. The geometric and kinematic features and the source properties of the earthquake were studied by Atzori et al (2009), Cirella et al (2009 and Walters et al (2009). It has been shown that the earthquake rupture very possibly was associated with the Paganica normal fault which strikes NW-SE and dips SW (Fig.…”

Section: Introductionmentioning

confidence: 99%

Strong foreshock signal preceding the L'Aquila (Italy) earthquake (Mw 6.3) of 6 April 2009

Papadopoulos

Charalampakis

Fokaefs

et al. 2010

103

Abstract. We used the earthquake catalogue of INGV extending from 1 January 2006 to 30 June 2009 to detect significant changes before and after the 6 April 2009 L'Aquila mainshock (M w =6.3) in the seismicity rate, r (events/day), and in b-value. The statistical z-test and Utsu-test were applied to identify significant changes. From the beginning of 2006 up to the end of October 2008 the activity was relatively stable and remained in the state of background seismicity (r=1.14, b=1.09). From 28 October 2008 up to 26 March 2009, r increased significantly to 2.52 indicating weak foreshock sequence; the b-value did not changed significantly. The weak foreshock sequence was spatially distributed within the entire seismogenic area. In the last 10 days before the mainshock, strong foreshock signal became evident in space (dense epicenter concentration in the hanging-wall of the Paganica fault), in time (drastic increase of r to 21.70 events/day) and in size (b-value dropped significantly to 0.68). The significantly high seismicity rate and the low b-value in the entire foreshock sequence make a substantial difference from the background seismicity. Also, the b-value of the strong foreshock stage (last 10 days before mainshock) was significantly lower than that in the aftershock sequence. Our results indicate the important value of the foreshock sequences for the prediction of the mainshock.