Antonella Cirella, Alessio Piatanesi, Elisa Tinti, Massimo Cocco Ground Motion and Source Process of the 6 th April 2009 L’Aquila, central Italy, Earthquake NERA Project- JRA3 (WP13) : INGV, Roma, May 2011 INGV

1.Global search kinematic inversion technique of seismological & geodetic data; 2. We retrieve the rupture process of the 2009 April 6 th L’Aquila, central Italy, mainshock (M w 6.1), by using a nonlinear separate and joint inversions of strong motion, GPS, DInSAR data; 3. In order to capture the heterogeneity of the rupture history, we give particular attention to the variability of model parameters and we attempt to constrain the local rupture velocity on the fault plane; 4. The goal is to constrain the mechanics of the causative fault as well as the observed ground motion. Goals NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

 joint and separate inversion of strong motion, GPS and DInSAR data;  several analytical slip velocity source time functions (STFs) are implemented; time functions (STFs) are implemented;  finite fault is divided into sub-faults; Inverted Parameters: Peak Slip Velocity; Peak Slip Velocity; Rise Time; Rise Time; Rupture Time; Rupture Time; Rake. Rake.  kinematic parameters are allowed to vary within a sub-fault; to vary within a sub-fault;  different crustal models can be adopted to compute Green's functions at different receivers. to compute Green's functions at different receivers. Kinematic Inversion Technique Data & Fault Parameterization  models having a local rupture velocity larger than P-wave velocity are discarded larger than P-wave velocity are discarded (not acausal rupture propagation); (not acausal rupture propagation); NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Kinematic Inversion Technique Output  Best Model  Average Model:  Standard Deviation: Output of kinematic inversion: Ω Model Ensemble Ω = Rupture Models m & Cost Function C(m) NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

1.The 2009 L’Aquila earthquake (M w 6.1) occurred in the Central Apennines (Italy) on April 6 th at the 01:32 UTC and caused nearly 300 casualties and heavy damages in the L’Aquila town and in several villages nearby. 2.The main shock ruptured a normal fault striking along the Apennine axis and dipping at nearly 50° to the SW. Most of the aftershocks are also associated with normal faulting, which is consistent with the present-day tectonic setting of this sector of the Apennines L’Aquila (central Italy) Earthquake, M w =6.1 NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Datasets: 2009 April 6 th 1:32 UTC  14 accelerograms (strong motion records from the RAN and the MedNet station AQU);  36 GPS stations (INGV-Ring, GNSSA, ISPRA, ITALPOS and ASI network, Cheloni & al, 2010 );    70 km;  frequency-band: (0.02÷0.5) Hz;  60 sec (body & surface waves); 2009 L’Aquila (central Italy) Earthquake, M w =6.1 Input NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

DInSAR  Satellite: Envisat descending. SAR Sensor: C-band, wavelength = 5.6 cm, look angle: 23°;  Each fringe represents a deformation of 2.8 cm in Line of Sight (LOS).  The images have been acquired on April 27, 2008 and April 12, 2009, respectively.  In green the 2625 resampled pixels (size=300 m) selected for the inversion. Input NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Crustal Structure Receiver function: 1D velocity model resulting from the analysis of receiver functions at AQU & AQG sites ( Bianchi & al., 2010 ). Used to compute synthetics at AQU and AQG. Receiver function: 1D velocity model resulting from the analysis of receiver functions at AQU & AQG sites ( Bianchi & al., 2010 ). Used to compute synthetics at AQU and AQG. nnCIA.mod: 1D velocity model resulting from the surface wave dispersion analysis ( Herrmann & Malagnini, 2009 ). Used to compute synthetics at all other stations. nnCIA.mod: 1D velocity model resulting from the surface wave dispersion analysis ( Herrmann & Malagnini, 2009 ). Used to compute synthetics at all other stations. Input NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Fault Geometry  hypocenter: 42.35°N, 13.38°E, 9.5km depth ( Chiarabba et al., 2009 );  strike: N133°E;  dip: 54° to SW;  all kinematic parameters are inverted simultaneously  (0-3.5) m/s psv; (0.75-3)s  ; ( )km/s vr; ( )° rake angle. Fault Parametrization  W=17.5km; L= 28km;  =3.5km; The proposed fault geometry agrees with the DInSAR data and the aftershock pattern. It is also consistent with both the hypocenter location and the induced surface breakages. The proposed fault geometry agrees with the DInSAR data and the aftershock pattern. It is also consistent with both the hypocenter location and the induced surface breakages. Input NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Inversion Results - Rupture History Output NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Inversion Results - Slip Velocity History Output NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Local Rupture Velocity & Rupture Index Mode Output Pulido & Dalguer (2009) NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

 We investigate the rupture history of the 2009 L’Aquila (Central Italy) earthquake using a nonlinear inversion of strong motion, GPS and DInSAR data.  Both the separate and joint inversions reveal a complex rupture history and a heterogeneous slip distribution characterized by a shallow slip patch located up-dip from the hypocenter and a large, deeper patch located southeastward.  The rupture history is characterized by two distinct phases: a rupture initiation with a modest moment release lasting nearly 0.5 sec, followed by a sharp increase in slip velocity and rupture speed (4.0 km/s) located 2 km up-dip from the hypocenter and a second stage (starting 2.0 sec after the nucleation) characterized by a slower along strike rupture propagation and the failure of the deep larger slip patch.  The up-dip and along-strike rupture propagations are separated in time and associated with two distinct rupture modes: Mode II and Mode III, respectively. Conclusions NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

 Our rupture model confirms the evident along strike directivity ( Pino&Di Luccio (2009), Akinci&al (2010)) and it also reveals an initial up-dip directivity that lasted for nearly 2sec and likely affected the ground motion observed in the L’Aquila town;  Our results show that the 2009 L’Aquila mainshock featured a very complex rupture history for a moderate M w 6.1, with strong spatial and temporal heterogeneities suggesting a strong frictional properties’ control of the rupture process. Cirella, A., A.Piatanesi, E. Tinti, M.Chini and M.Cocco, Source Complexity of the 2009 L’Aquila, Italy, earthquake: Evidence for a Rheological Control on Rupture Process, submitted to Geophysical Journal International. Cirella, A., A.Piatanesi, M.Cocco, E. Tinti, L. Scognamiglio, A. Michelini, A. Lomax and E.Boschi (2009), Rupture history of the 2009 L'Aquila (Italy) earthquake from non-linear joint inversion of strong motion and GPS data, Geophys. Res. Lett., 36, L19304, doi: /2009GL for details see.. NERA Project- JRA3 (WP13) : INGV, Roma, May 2011 Conclusions

Slip Velocity History-Directivity

 To investigate the relationship between the observed ground motion variability & the kinematic source parameters taking into account the strong heterogeneity of the rupture process;  To study the effects of the observed directivity;  To better analyze the effect of frictional properties on the retrieved rupture history;  These aspects are crucial to generate & to interpret shaking scenarios in near source regions. Key Issues This afternoon.. 13:45 – 14:00 Task 2 “Identification of ground motion dominated by the source” (A. Piatanesi - INGV) NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Kinematic Inversion Technique Stage I: Building-up the Model Ensemble random model m0 START + = Strong motion L1+L2 norm To quantify the misfit… GPS L2 norm C(m) DInSAR L2 norm + Forward Modeling: Compsyn Misfit computation Loop over parameters (Vr,…) Loop over model values Loop over iterations Loop over temperatures end Simulated annealing Heat-bath algorithm Aux NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Inversion Results - DataFit Aux NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Inversion Results - DataFit only DInSAR & only GPS Aux

Inversion Results - DataFit: only SM Aux NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

Inversion Results - Snapshots Aux NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

2009 L’Aquila (Central Italy) Earthquake, M w =6.1 Rupture Process & on-fault Seismicity Pattern NERA Project- JRA3 (WP13) : INGV, Roma, May 2011

is the angle between the rupture velocity vector and the fault strike direction NERA Project- JRA3 (WP13) : INGV, Roma, May 2011