Antonella Cirella, Alessio Piatanesi, Massimo Cocco, Elisa Tinti, Laura Scognamiglio, Alberto...

Antonella Antonella Cirella,Cirella,

Alessio Alessio Piatanesi, Piatanesi,

Massimo Cocco, Massimo Cocco,

Elisa Tinti, Elisa Tinti,

Laura Laura Scognamiglio,Scognamiglio,

Alberto Alberto Michelini, Michelini,

Anthony Lomax Anthony Lomax

INGV

The rupture history of the 2009 L’Aquila The rupture history of the 2009 L’Aquila earthquake by non-linear joint inversion earthquake by non-linear joint inversion of strong motion and GPS dataof strong motion and GPS data

Convegno Annuale dei Progetti Sismologici, Roma, Convegno Annuale dei Progetti Sismologici, Roma, 19-21 Ottobre 200919-21 Ottobre 2009

Precaria assegno di ricerca- scadenza 31/12/2009

Precaria art.23 - scadenza 31/07/2010

Precaria art.23 - scadenza 30/11/2009

1.1. The 2009 L’Aquila earthquake (MThe 2009 L’Aquila earthquake (Mww 6.3) occurred in the 6.3) occurred in the Central Apennines (Italy) on April 6Central Apennines (Italy) on April 6thth at the 01:32 UTC at the 01:32 UTC and caused nearly 300 casualties and heavy damages in and caused nearly 300 casualties and heavy damages in the L’Aquila town and in several villages nearby.the L’Aquila town and in several villages nearby.

2.2. The main shock ruptured a normal fault striking along The main shock ruptured a normal fault striking along the Apennine axis and dipping at nearly 50° to the the Apennine axis and dipping at nearly 50° to the SW. Most of the aftershocks are also associated with SW. Most of the aftershocks are also associated with normal faulting, which is consistent with the present-normal faulting, which is consistent with the present-day tectonic setting of this sector of the Apennines.day tectonic setting of this sector of the Apennines.

3.3. The 2009 L’Aquila earthquake provided the collection The 2009 L’Aquila earthquake provided the collection of an excellent data set of seismograms and geodetic of an excellent data set of seismograms and geodetic data for a normal faulting event.data for a normal faulting event.

4.4. In this study, we investigate the rupture process of In this study, we investigate the rupture process of the L’Aquila main shock by using a nonlinear joint the L’Aquila main shock by using a nonlinear joint inversion of strong motion and GPS data.inversion of strong motion and GPS data.

5.5. The goal is to constrain the rupture history to better The goal is to constrain the rupture history to better understand the mechanics of the causative fault as well understand the mechanics of the causative fault as well as the observed ground shaking.as the observed ground shaking.

Goals:Goals:


Kinematic Inversion Technique:Kinematic Inversion Technique:

Data & Fault ParameterizationData & Fault ParameterizationKinematic Inversion Technique:Kinematic Inversion Technique:

Data & Fault ParameterizationData & Fault Parameterization

1) joint inversion of strong motion and GPS 1) joint inversion of strong motion and GPS data;data;

4) several analytical slip 4) several analytical slip velocity source time functions velocity source time functions (STFs) are implemented. (STFs) are implemented.

2) finite fault is divided into 2) finite fault is divided into sub-faults;sub-faults;

Inverted Inverted Parameters:Parameters:

•Peak Slip Peak Slip Velocity;Velocity;

•Rise Time;Rise Time;

•Rupture Rupture Velocity;Velocity;

•Rake.Rake.

3) kinematic parameters are allowed to vary 3) kinematic parameters are allowed to vary within a sub-fault;within a sub-fault;


5) different crustal models can be 5) different crustal models can be adopted adopted to compute Green's functions at to compute Green's functions at different receivers.different receivers.

Kinematic Inversion Technique :Kinematic Inversion Technique :

Stage I: Building Model Ensemble–HB Simulated Stage I: Building Model Ensemble–HB Simulated AnnealingAnnealing


Stage I: Building Model Ensemble–HB Simulated Stage I: Building Model Ensemble–HB Simulated AnnealingAnnealing

Forward Modeling: DWFE Method - Compsyn Forward Modeling: DWFE Method - Compsyn (complete response 1D vertically varying(complete response 1D vertically varying

Earth Structure)Earth Structure)

random model m0random model m0STARTSTART

loop over parameters N (Vr,rise time,…)loop over parameters N (Vr,rise time,…)Loop over model values MLoop over model values M

+=Strong motion L1+L2 norm

To quantify the misfit…

GPSL2 norm

C(m)C(m)



Stage II: Appraisal of the EnsembleStage II: Appraisal of the EnsembleKinematic Inversion Technique :Kinematic Inversion Technique :

Stage II: Appraisal of the EnsembleStage II: Appraisal of the Ensemble

Best Model Best Model

Output of kinematic Output of kinematic inversion:inversion:

Cos

t F

unct

ion

Cos

t F

unct

ion

iterationsiterations

ΩΩRupture Models Rupture Models m m &&

Cost Function Cost Function C(m)C(m)

Model Ensemble Model Ensemble ΩΩ = =


Average Model:Average Model:

Standard Deviation:Standard Deviation:

Kinematic Inversion:Kinematic Inversion: 2009 L’Aquila (Central Italy) Earthquake, M2009 L’Aquila (Central Italy) Earthquake, Mww=6.3=6.3

Data:Data: 2009 April 6th 1:32 2009 April 6th 1:32 UTCUTC


14 accelerograms 14 accelerograms (strong motion records (strong motion records from the RAN and the from the RAN and the MedNet station AQU);MedNet station AQU);

17 GPS stations 17 GPS stations (INGV-Ring & ASI (INGV-Ring & ASI network) ;network) ;

70 km;70 km;

frequency-band: frequency-band: (0.02÷0.5) Hz; (0.02÷0.5) Hz;

60 sec (body & surface 60 sec (body & surface waves);waves);


Crustal Crustal Structure:Structure:

1D velocity model 1D velocity model resulting from the analysis resulting from the analysis of receiver functions at of receiver functions at AQU & AQG sites (AQU & AQG sites (I. I. Bianchi, pers comm, 2009Bianchi, pers comm, 2009););

a regional 1D velocity a regional 1D velocity model obtained by model obtained by Bagh et Bagh et al.al. (2007) inverting P-wave (2007) inverting P-wave arrival times of digital arrival times of digital waveforms (INGV networks);waveforms (INGV networks);

shallow low velocity shallow low velocity layer (vlayer (vp p 4km/s) 4km/s) consistent with surface consistent with surface wave dispersion analysis wave dispersion analysis ((Malagnini & Hermann, pers Malagnini & Hermann, pers comm, 2009comm, 2009).).


Kinematic Inversion:Kinematic Inversion: 2009 L’Aquila (Central Italy) Earthquake, 2009 L’Aquila (Central Italy) Earthquake,

MMww=6.3=6.3Fault Fault Geometry:Geometry: hypocenter: 42.35°N, 13.38°E, 9.5km depth hypocenter: 42.35°N, 13.38°E, 9.5km depth ((Chiarabba et al., 2009Chiarabba et al., 2009););

strike: N133°E;strike: N133°E;

dip: 54° to SW; dip: 54° to SW;

all kinematic parameters are inverted all kinematic parameters are inverted simultaneouslysimultaneously (0-2.5) m/s psv; (1-2)s (0-2.5) m/s psv; (1-2)s ; (1.8-2.8)km/s vr; ; (1.8-2.8)km/s vr; (250-290)° rake angle.(250-290)° rake angle.

Fault Parametrization:Fault Parametrization: W=17.5km; L= 28km; W=17.5km; L= 28km; =3.5km;=3.5km;


The proposed fault The proposed fault geometry agrees with the geometry agrees with the InSAR data and the aftershock InSAR data and the aftershock pattern. It is also pattern. It is also consistent with both the consistent with both the hypocenter location and the hypocenter location and the induced surface breakages. induced surface breakages.


Rupture Process - Inversion Rupture Process - Inversion ResultsResults

MMo o = 3.5 = 3.5 10 101818 NmNmMMo o = 3.5 = 3.5 10 101818 NmNm


Data Fit - Inversion Data Fit - Inversion ResultsResults

2009 L’Aquila (Central Italy) Earthquake, M2009 L’Aquila (Central Italy) Earthquake, Mww=6.3=6.3

Local Rupture VelocityLocal Rupture Velocity


VVr r 2.8 - 3.0 2.8 - 3.0 km/skm/s

VVr r 1.8 - 2.2 1.8 - 2.2 km/skm/s


Rupture Velocity & Crustal StructureRupture Velocity & Crustal Structure


I. Bianchi, personal comm., 2009

1.6 km/s1.6 km/s

2.7 km/s2.7 km/s

4 km/s4 km/s

3.2 km/s3.2 km/s


Rupture Process & on-fault Seismicity Pattern Rupture Process & on-fault Seismicity Pattern


ConclusionsConclusions We image the rupture history of the 2009 L’Aquila We image the rupture history of the 2009 L’Aquila

(Central Italy) earthquake using a nonlinear joint (Central Italy) earthquake using a nonlinear joint inversion of strong motion and GPS data. inversion of strong motion and GPS data.

The inferred slip distribution is heterogeneous and The inferred slip distribution is heterogeneous and characterized by a small, shallow slip patch located characterized by a small, shallow slip patch located up-dip from the hypocenter (9.5 km depth) and a large, up-dip from the hypocenter (9.5 km depth) and a large, deeper patch located southeastward. deeper patch located southeastward.

The rupture velocity is larger in the up-dip than in The rupture velocity is larger in the up-dip than in the along-strike direction. This difference can be the along-strike direction. This difference can be partially accounted by the crustal structure, which is partially accounted by the crustal structure, which is characterized by a high velocity layer above the characterized by a high velocity layer above the hypocenter and a lower velocity below. hypocenter and a lower velocity below.

The imaged slip distribution correlates well with the The imaged slip distribution correlates well with the on-fault aftershock pattern as well as with mapped on-fault aftershock pattern as well as with mapped surface breakages.surface breakages.

Cirella, A., A.Piatanesi, M.Cocco, E. Tinti, L. Scognamiglio, A. Cirella, A., A.Piatanesi, M.Cocco, E. Tinti, L. Scognamiglio, A. Michelini, A. Lomax and E.Boschi (2009), Rupture history of the 2009 Michelini, A. Lomax and E.Boschi (2009), Rupture history of the 2009 L'Aquila (Italy) earthquake from non-linear joint inversion of strong L'Aquila (Italy) earthquake from non-linear joint inversion of strong motion and GPS data, motion and GPS data, Geophys. Res. LettGeophys. Res. Lett., 36, L19304, ., 36, L19304, doi:10.1029/2009GL039795doi:10.1029/2009GL039795

Un ringraziamento speciale ai Vigili del Fuoco, ai volontari della Protezione Civile ed ai lavoratori precari dell’INGV che per tutta la durata dello stato di emergenza hanno continuato e continuano a garantire con il massimo impegno le attività tecnico/scientifiche, specie quelle di monitoraggio.

Agli aquilani, per tutto quello che ancora c’è da fare…

ReferencesReferencesAnzidei, M., Boschi, E., Cannelli, V., Devoti, R., Esposito, A., Galvani, A., Melini, D., Pietrantonio, G., Riguzzi, F., Sepe, V., and E. Serpelloni (2009), Coseismic deformation of the destructive April 6, 2009 L'Aquila earthquake (central Italy) from GPS data, Geophys. Res. Lett., doi: 10.1029/2009GL039145.

Atzori, S., Hunstad, I., Chini, M., Salvi, S., Tolomei, C., Bignami, C., Stramondo, S., Trasatti, E. Antonioli, A. and E. Boschi (2009), Finite fault inversion of DInSAR coseismic displacement of the 2009 L’Aquila earthquake (Central Italy), Geophys. Res. Lett., doi: 10.1029/2009GL039293.

Bagh, S., L. Chiaraluce, P. De Gori, M. Moretti, A. Govoni, C. Chiarabba, P. Di Bartolomeo, M. Romanelli (2007), Background seismicity in the Central Apennines of Italy: The Abruzzo region case study, Tectonophysics, 444, 80-92.

Chiarabba, C., A. Amato, M. Anselmi, P. Baccheschi, I. Bianchi, M. Cattaneo, G. Cecere, L. Chiaraluce, M. G. Ciaccio, P. De Gori, G. De Luca, M. Di Bona, R. Di Stefano, L. Faenza, A. Govoni, L. Improta, F. P. Lucente, A. Marchetti, L. Margheriti, F. Mele, A. Michelini, G. Monachesi, M. Moretti, M. Pastori, N. Piana Agostinetti, D. Piccinini, P. Roselli, D. Seccia, and L. Valoroso (2009), The 2009 L'Aquila (central Italy) MW6.3 earthquake: Main shock and aftershocks, Geophys. Res. Lett., 36, L18308, doi:10.1029/2009GL039627

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:10.1029/2009GL039795

EMERGEO WORKING GROUP (2009), Evidence for surface rupture associated with the Mw 6.3 L'Aquila earthquake sequence of April 2009 (central Italy), submitted to

Terranova.

Piatanesi, A., A. Cirella, P. Spudich, and M. Cocco (2007), A global search inversion for earthquake kinematic rupture history: Application to the 2000 western Tottori, Japan earthquake, J. Geophys. Res., 112, B07314, doi:10.1029/2006JB004821.

-The strike direction agrees with the InSAR data;

- The selected dip angle is consistent with both the hypocenter location and the surface breakages observed near Paganica.

The proposed fault geometry:

- agrees with the relocated aftershocks, availed of manually picked INGV bulletin arrival time data;

- lie within the range of values inferred from moment tensor solutions.Convegno Annuale dei Progetti Sismologici, Roma, Convegno Annuale dei Progetti Sismologici, Roma,

19-21 Ottobre 200919-21 Ottobre 2009

2.5491 cm/s 11.3967cm/s

2.7685 cm/s

6.6854 cm/s


Rupture Directivy & Observed PGVRupture Directivy & Observed PGV


Seismic StationsANT: Agency: RAN

Lat: 42.4182 Lon: 13.0786 Distance: 21.7 kmStation Comp Max Vel (cm/s) Max Acc (%g)

HNE 1.7646 2.0102 HNZ 1.1741 1.1721 HNN 2.5491 2.6341

AQU: Agency: IVLat: 42.3539 Lon: 13.4019 Distance: 0.0 km

Station Comp Max Vel (cm/s) Max Acc (%g) HNE 25.6389 32.8408 HNZ 32.2634 41.7600 HNN 38.5778 39.5897

CLN: Agency: RANLat: 42.0852 Lon: 13.5207 Distance: 22.3 km

Station Comp Max Vel (cm/s) Max Acc (%g) HNE 4.7703 8.0816 HNZ 7.0866 4.5887 HNN 6.6854 8.9818 FMG: Agency: RAN

Lat: 42.2680 Lon: 13.1172 Distance: 19.0 kmStation Comp Max Vel (cm/s) Max Acc (%g) HNE 2.7685 2.3882 HNZ 1.2667 1.9756 HNN 1.6637 2.6862

GSA: Agency: RANLat: 42.4207 Lon: 13.5194 Distance: 11.2 km

Station Comp Max Vel (cm/s) Max Acc (%g) HNE 11.3967 14.8838 HNZ 4.2237 10.9188 HNN 7.9026 14.5186

http://earthquake.rm.ingv.it/shakemap/shake/2206496920/intensity.html


Total Slip & Crustal StructureTotal Slip & Crustal Structure


Auxiliary Material 1 Auxiliary Material 1

Strong motion L1+L2 norm

GPS L2 norm

Hudnut et al., Hudnut et al., 19961996

Spudich & Miller, Spudich & Miller, 19901990

Auxiliary Auxiliary Material 2 Material 2 - Earthquake locationsEarthquake locations

In our study we have adopted the INGV revised main shock hypocenter location (Chiarabba et al, 2009). We note, however, that the horizontal and vertical errors (0.1 and 0.2 km, respectively) published on the web page and provided by the Hypoellipse programme likely underestimate the true location uncertainties. To appraise the solution, we have applied the global search, non-linear location algorithm NonLinLoc (Lomax, 2005; Lomax et al. 2001; Lomax et al. 2000) to 30 manually picked phases. The resulting axes of the dispersion ellipsoid feature lengths of 0.4, 0.45 and 0.83 km and a root mean square of the arrival time residuals of 0.071 s. The hypocenter location used in this study was found to lie within the probability density function scatter values. In addition, in this study we have used the same non-linear inversion algorithm to locate early aftershocks and to select those situated near the main shock fault plane. ReferencesLomax, A., J. Virieux, P. Volant and C. Berge, 2000. Probabilistic earthquake Lomax, A., J. Virieux, P. Volant and C. Berge, 2000. Probabilistic earthquake location in 3D and layered models: Introduction of a Metropolis-Gibbs method and location in 3D and layered models: Introduction of a Metropolis-Gibbs method and comparison with linear locations, in Advances in Seismic Event Location Thurber, comparison with linear locations, in Advances in Seismic Event Location Thurber, C.H., and N. Rabinowitz (eds.), Kluwer, Amsterdam, 101-134..C.H., and N. Rabinowitz (eds.), Kluwer, Amsterdam, 101-134..

Lomax, A., A. Zollo, P. Capuano, and J. Virieux, 2001. Precise, absoute earthquake Lomax, A., A. Zollo, P. Capuano, and J. Virieux, 2001. Precise, absoute earthquake location under Somma-Vesuvius volcano using a new 3D velocity model, Gephys. J. location under Somma-Vesuvius volcano using a new 3D velocity model, Gephys. J. Int., 146, 313-331.Int., 146, 313-331.

Lomax, A. (2005). A reanalysis of the hypocentral location and related Lomax, A. (2005). A reanalysis of the hypocentral location and related observations for the great 1906 California earthquake, Bull. Seismol. Soc. Am., observations for the great 1906 California earthquake, Bull. Seismol. Soc. Am., 95, 861–877. 95, 861–877.

Auxiliary Material 3 Auxiliary Material 3 - Synthetic Test Synthetic Test

Synthetic data are generated using a target rupture model Synthetic data are generated using a target rupture model obtained by assumig a regularized Yoffe function with Tacc obtained by assumig a regularized Yoffe function with Tacc (time to peak slip velocity) equal to 0.225 sec. Slip is (time to peak slip velocity) equal to 0.225 sec. Slip is concentrated only on one main asperity, characterized by a peak concentrated only on one main asperity, characterized by a peak slip velocity of 1.5 m/s and a rise time of 2.5 s. The rake slip velocity of 1.5 m/s and a rise time of 2.5 s. The rake angle is fixed equal to 270°. The rupture front propagates at angle is fixed equal to 270°. The rupture front propagates at 2.2 km/s, except in the portion of the fault located between 6 2.2 km/s, except in the portion of the fault located between 6 km SE from the nucleation and the right edge of the fault km SE from the nucleation and the right edge of the fault plane, where it accelerates to nearly 2.8 km/s. We invert plane, where it accelerates to nearly 2.8 km/s. We invert simultaneously the kinematic parameters (peak slip velocity, simultaneously the kinematic parameters (peak slip velocity, rise time and rupture time) at nodal points equally spaced rise time and rupture time) at nodal points equally spaced along strike and dip every 3.5 km. We compute synthetic ground along strike and dip every 3.5 km. We compute synthetic ground velocities in the frequency band 0.02 and 0.5 Hz and horizontal velocities in the frequency band 0.02 and 0.5 Hz and horizontal and vertical components of static displacement and we use these and vertical components of static displacement and we use these as our target dataset. During the inversion, the peak slip as our target dataset. During the inversion, the peak slip velocity is allowed to vary between 0 and 2.5 m/s with 0.25 m/s velocity is allowed to vary between 0 and 2.5 m/s with 0.25 m/s interval; the rise time between 1.0 and 3.0 sec at 0.25 sec interval; the rise time between 1.0 and 3.0 sec at 0.25 sec step increment and the rupture time of each grid node is step increment and the rupture time of each grid node is bounded by a rupture velocity ranging between 2 and 3 km/s. The bounded by a rupture velocity ranging between 2 and 3 km/s. The rake angle is kept fixed. We apply a two stages nonlinear rake angle is kept fixed. We apply a two stages nonlinear global inversion technique [see Piatanesi et al., 2007].global inversion technique [see Piatanesi et al., 2007].The synthetic test proves that the azimuthal coverage of the The synthetic test proves that the azimuthal coverage of the selected stations is good enough to obtain reliable results.selected stations is good enough to obtain reliable results.

Auxiliary Material 3:Auxiliary Material 3:

Synthetic TestSynthetic Test

Tacc must be much shorter than the rise time. In this inversion attempt we have chosen a value of the Tacc parameter (0.225 sec) that is consistent with the relatively short rise time (ranging between 1 and 2 sec) expected for a moderate magnitude earthquake and it is close to previous applications of the Yoffe function (Cirella et al., 2008). We have verified that, in the frequency band used in this study (0.02-0.5 Hz), changing the adopted value (between 0.225 and 0.4 sec) does not affect the spatial distribution of slip and rupture times and the effect on the rise time is very modest. The choice of Tacc influences the inferred peak slip velocity value (see equation 7 in that paper). For the L’Aquila earthquake the inversion of available data with Tacc equal to 0.225 or 0.4 sec yields a decrease of maximum peak slip velocity of nearly 12 %.

Tacc

Regularized Yoffe Regularized Yoffe Tacc=0.2secTacc=0.2sec

Regularized Yoffe Regularized Yoffe Tacc=0.4secTacc=0.4sec

Box-carBox-carCosineCosine


Rupture Process & on-fault Seismicity Pattern Rupture Process & on-fault Seismicity Pattern


Antonella Cirella, Alessio Piatanesi, Massimo Cocco, Elisa Tinti, Laura Scognamiglio, Alberto...

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