Gravitational deformation after the April 6, 2009 L Aquila Earthquake detected by Cosmo-SkyMed

Transcription

1 Gravitational deformation after the April 6, 2009 L Aquila Earthquake detected by Cosmo-SkyMed Christian Bignami 1 ; Matteo Albano 1 ; Salvatore Barba 1 ; Mario Costantini 2 ; Fabio Malvarosa 2 ; Marco Moro 1 ; Michele Saroli 3 ; Salvatore Stramondo 1 1: Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy. 2: E-GEOS S.p.A., Rome, Italy. 3: DICeM Dipartimento di Ingegneria Civile e Meccanica - University of Cassino and Southern Lazio, Cassino (FR), Italy.

2 Contents L Aquila earthquake Previous studies Earthquake-related deformation InSAR data COSMO-SkyMed dataset Postseismic deformation Numerical modelling Results Conclusions

3 L Aquila earthquake On April 6th, 2009, a normal faulting earthquake of M w 6.3 hit the central Apennines, provoking severe damages to the city of L Aquila and neighbouring villages. The mainshock nucleated at a depth of about 9 km, 4 km southwest of the city of L Aquila, dislocating the Paganica Fault (PF). The mainshock was preceded by foreshocks up to M w 4.3 and followed by a 3-year-long aftershock sequence, more than 80 thousands events among which seven with M w >5. April 6,2009 Mw 6,1

4 Previous studies Coseismic deformations GPS; InSAR (Anzidei et al, 2009; Serpelloni et al, 2012; Atzori et al., 2009; Trasatti et al., 2011; Volpe et al., 2012) Analytical models Numerical models (FEM) Postseismic deformations Atzori et al., 2009 GPS; InSAR; levelling (D Agostino et al., 2009; Cheloni et al., 2010; D Agostino et al., 2012; Gualandi et al., 2014; Cheloni et al., 2014) Max timespan = 10 months Analytical models Prevalent tectonic origin D Agostino et al., 2012

5 Earthquake-related deformations Pollitz et al., ) Slip on or contiguous to the mainshock rupture 3) Poro-elastic rebound due to pore-fluid flow Cheloni et al., ) Visco-elastic relaxation in the lower crust and upper mantle Lacroix et al., 2011 Jònsson et al., ) Surficial deformations on areas with high energy relief

6 Earthquake-related deformations Surficial deformations on areas with high energy relief Coseismic deformation L Aquila earthquake (Moro et al, 2011) Postseismic deformation Surficial deformations, triggered by the earthquake, but driven by gravity

7 InSAR dataset COSMO-SkyMed Persistent Scatterer Pair technique (PSP) (Costantini et al., 2008, 2013, 2014) Timespan 16 months (April 12, 2009 August 6, 2010) Images 35 Sensor X 9.6 Ghz Mode Stripmap Resolution 3 m per pixel Orbit Ascending Incidence angle 40

8 Postseismic deformation Displacement field at August 6, 2010 Shallow afterslip of the PF

9 Postseismic deformation Displacement field at August 6, 2010 Section A Section B Convexity over Mt. Ocre ridge

10 Postseismic deformation Displacement field at August 6, 2010 Double crest Limestone Flysch Gravitational deformation (Salvi & Nardi, 1995; Salvi et al., 2003) Reactivation after the earthquake

11 Numerical modelling Finite element models Section A Section B Displacement mainly directed orthogonally to the ridge axis

12 Numerical modelling Homogeneous isotropic material Constitutive model Linear elastic (ELA) Linear elastic perfectly plastic (PLA) Modelling phases PF 1) Gravity load In-situ stresses 2) Coseismic (t=0) Istantaneous downward movement (cm) Coseismic displacement profile 3) Postseismic (t=16 months) Constant velocity downward movement (mm/year) Postseismic displacement time series

13 Results Ocre ridge 1 2 Section A Cosesismic displacement profile Point 1 Postseismic displacement profile (August 6, 2010) Point 2

14 Results Ocre ridge Section B Point 1 Cosesismic displacement profile Point 2 Postseismic displacement profile (August 6, 2010) Point 3

15 Results Postseismic resultant displacements (August 6, 2010)

16 Conclusions We investigated the postseismic effects of the April 6, L Aquila earthquake by numerical modelling and InSAR data. We observed that the elasto-plastic behaviour of the material satisfactorily describes the observed displacements The change in the coseismic stress and geometry destabilized the Mt. Ocre ridge, causing an excess of displacements with respect to the L Aquila plain To analyse InSAR data on descending orbit To implement a nonlinear afterslip

17 Conclusions