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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 AlpineApenninic region
Task Groups: TG Planetary Scale
Cooperation: LMU München, Germany; IAG Granada, Spain
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
www.spice-rtn.org
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
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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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 x86 Linux cluster)
C) Inverse problem: partial derivatives of the 3D Green functions are
computed to invert observed broad-band seismograms for the seismic
moment tensor.
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
www.spice-rtn.org
Example: The Mw 5.0, 24.11.2004 Salò earthquake (northern Italy)
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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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)
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
www.spice-rtn.org
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
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
www.spice-rtn.org
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
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
)
Mw = 5.0, depth =7.5 km
Reverse faulting source
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Resolution of source parameters: Depth
Longer period band, low resolution
Shorter period band, high resolution
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
www.spice-rtn.org
Resolution of source parameters: Depth, mechanism and source type
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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The Salò earthquake: waveform fits (35s – 15s period band)
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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The Salò earthquake: waveform modelling at the RETREAT transect
Temporary broad-band stations from the
Po plain to the island of Elba.
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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The Salò earthquake: waveform modelling at the RETREAT transect
matches of vertical (top) and
transverse (bottom) displacement
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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The Salò earthquake: waveform modelling at the RETREAT transect
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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Late surface wave arrivals in the Alpine area
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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Late surface wave arrivals in the Alpine area
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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Late surface wave arrivals in the Alpine area
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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Late surface wave polarizations for the 2004 Slovenia earthquake
Love wave back-azimuths converge towards south ->
Reflection from the Northern Apennines?
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
www.spice-rtn.org
Late surface wave arrivals in the Tyrrhenian Sea
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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Deep crustal structure along the RETREAT transect
Moho offset responsible for reflection?
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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Spectral element modelling of late arrivals: 1D model with moho offset
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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Spectral element modelling of late arrivals: evolution of wave fields
17.07.2001 Meran earthquake
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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Spectral element modelling of late arrivals: evolution of wave fields
12.07.2004 Slovenia earthquake
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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Spectral element modelling of late arrivals: waveform matches
North, east and vertical coda
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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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?
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
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