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S eismic wave P ropagation and I maging in C omplex media: a E uropean network

S eismic wave P ropagation and I maging in C omplex media: a E uropean network. Daniel Stich Experienced Researcher Host Institution: INGV Bologna Place of Origin: Munich, Germany Appointment Time: June 2005

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S eismic wave P ropagation and I maging in C omplex media: a E uropean network

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  1. Seismic wave Propagation and Imaging in Complex media: a European network • Daniel Stich • Experienced Researcher • Host Institution: INGV Bologna • Place of Origin: Munich, Germany • Appointment Time: June 2005 • Project: Spectral element waveform modeling in the Alpine-Apenninic region • Task Groups: TG Planetary Scale • Cooperation: LMU München, Germany; IAG Granada, Spain

  2. A) Spectral element moment tensor inversion in a 3D a priori earth model for the Alpine-Apenninic region B) Reflection of seismic surface waves at the Northern Apennines

  3. Moment tensor inversion in a 3D model for the Alpine-Apenninic region - Objective: Consider 3D wave propagation effects in regional moment tensor inversion within the heterogeneous Alpine-Apenninic area A) Synthesize a regional a priori lithosphere model from available regional seismological, seismic and gravimetric studies B) Spectral element code SPECFEM3D (Komatitsch and Tromp, 2002a,b) is used for numerical simulation of seismic wave propagation in the 3D regional model (16°x16° lateral model dimensions, ~16kmx16kmx10km elements in the crust, 5min seismograms, 3h of computation on 49 cpu of the INGV 32bit x86Linux cluster) C) Inverse problem: partial derivatives of the 3D Green functions are computed to invert observed broad-band seismograms for the seismic moment tensor.

  4. Example: The Mw 5.0, 24.11.2004 Salò earthquake (northern Italy)

  5. The regional 3D earth model 1D layered crustal structures assigned to 0.5°x0.5°blocks + 3D global mantle model (Ritsema et al. 1999) + lateral smoothing (50km) Depth to Moho (15 – 50 km) Average S-wave velocity in the upper 20km (3.2 -3.5 km/s)

  6. Inversion: Moment tensor of the 2004 Salò earthquake (Italy) -We invert time domain displacement waveforms for the seismic moment tensor by minimizing the L2-norm misfit between observed and predicted waveforms -The source depth is determined independently by a grid search over trial depths (8 depths -> 8 x 6 x 3h ~ 6 days for total computation) -No weighting or alignment of individual waveforms is used in inversion

  7. Inversion: Moment tensor of the 2004 Salò earthquake (Italy) Inversion in 4 different period bands: B1: 100s – 35s (like MedNet RCMT) B2: 70s – 25s (like ETH solution) B3: 50s – 20s B4: 35s – 15s ) Mw = 5.0, depth =7.5 km Reverse faulting source

  8. Resolution of source parameters: Depth Longer period band, low resolution Shorter period band, high resolution

  9. Resolution of source parameters: Depth, mechanism and source type

  10. The Salò earthquake: waveform fits (35s – 15s period band)

  11. The Salò earthquake: waveform modelling at the RETREAT transect Temporary broad-band stations from the Po plain to the island of Elba.

  12. The Salò earthquake: waveform modelling at the RETREAT transect matches of vertical (top) and transverse (bottom) displacement

  13. The Salò earthquake: waveform modelling at the RETREAT transect

  14. Late surface wave arrivals in the Alpine area

  15. Late surface wave arrivals in the Alpine area

  16. Late surface wave arrivals in the Alpine area

  17. Late surface wave polarizations for the 2004 Slovenia earthquake Love wave back-azimuths converge towards south -> Reflection from the Northern Apennines?

  18. Late surface wave arrivals in the Tyrrhenian Sea

  19. Deep crustal structure along the RETREAT transect Moho offset responsible for reflection?

  20. Spectral element modelling of late arrivals: 1D model with moho offset

  21. Spectral element modelling of late arrivals: evolution of wave fields 17.07.2001 Meran earthquake

  22. Spectral element modelling of late arrivals: evolution of wave fields 12.07.2004 Slovenia earthquake

  23. Spectral element modelling of late arrivals: waveform matches North, east and vertical coda

  24. Reflection of seismic surface waves at the Northern Apennines - Surface waves are reflected at the northern Apennines Moho step. - Reflections are large in amplitude and a relevant contribution to the regional wave field -> complications in seismological data analysis - Further modelling: Can reflected surface waves be useful to constrain deep lithospheric structure?

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