Advances in the Science and Applications of SAR Interferometry ESA ESRIN 30th November - 4th December 2009 Frascati, Italy
Interseismic deformation along the 1908 earthquake normal fault in the Straits of Messina, measured by means of SBAS ERS/ENVISAT time series Cristiano Tolomei, Simone Atzori and Stefano Salvi Istituto Nazionale di Geofisica e Vulcanologia
Research funded by the ASI-SIGRIS project
The Straits of Messina The largest earthquake of the XX century in Italy Mw = 7.1 Debated earthquake source (6 different fault models proposed) To be crossed by a 4-km long suspended bridge
From Amoruso et al, 2002, JGR
Advances in the Science and Applications of SAR Interferometry ESA ESRIN, 30th November - 4th December 2009 Frascati, Italy
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SAR data for SBAS processing Descending dataset • 71 ERS images from May 1992, to July 2002 • 183 interferograms Ascending dataset • 37 ERS + 34 ENVISAT images from September 1992, to April 2008 • 181 interferograms Baseline constraints
Multi-temporal Differential SAR Interferometry (SBAS) algorithm (Berardino P., Fornaro G., Lanari R.,Sansosti E., IEEE, 2002).
Bt = 1200 days Bn = 200 meters
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LoS Ground Velocity Maps
Descending orbit
Ascending orbit Reference point
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Time Series examples Ascending case
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CGPS reference point - TGRC Courtesy, Serpelloni (INGV-Bo), 2008
TGRC GPS site displacements (2000-2008) along E, N and Up directions (in black) and along the ascending ERS LoS (in green).
SAR displacement time series at TGRC, scaled to the GPS LoS time series.
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LoS Scaled ground velocity maps
Ascending orbit
Descending orbit
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Up component
Based on the GPS velocity field, we assume the North velocity = 1mm/yr Advances in the Science and Applications of SAR Interferometry ESA ESRIN, 30th November - 4th December 2009 Frascati, Italy
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SAR East velocity field in agreement with GPS
East Component
GPS velocities w.r.t. MTTG
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Modeling We test if the observed velocities can be interpreted in term of interseismic strain accumulation along the 1908 earthquake fault. We first re-model the 1908 seismic dislocation using coseismic observations from a 1907-1909 levelling line (about 100 benchmarks).
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The 1908 seismic source
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1908 source parameters Length (m)
Width (m)
Depth (m)
Strike (deg)
Dip (deg)
East (m)
North (m)
Rake (deg)
Slip (cm)
29706
18211
2269
‐7.3
42
556736
4215388
‐125.2
135.5
Advances in the Science and Applications of SAR Interferometry ESA ESRIN, 30th November - 4th December 2009 Frascati, Italy
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Interseismic deformation modeling Method: We inverted the SAR LoS velocity data using an elastic dislocation model (Okada, 1985) for an infinite dislocation. Results: We cannot obtain a good fit to the observations using a 1908-type dislocation. We obtain a good fit (RMS ~ 1 mm/yr) using a slightly different source
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Interseismic deformation modeling Ascending modeled velocity
Ascending observed velocity
Length (m)
Width (m)
Depth (m)
Strike (deg)
Dip (deg)
East (m)
North (m)
Rake (deg)
Slip (cm)
500000
100000
9051
10
70
542690
4218000
‐125
0.5
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Interseismic vs coseismic source
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Residuals & profile Ascending case
Descending case
Residuals (ascending): RMS = 1.08 mm/yr Advances in the Science and Applications of SAR Interferometry ESA ESRIN, 30th November - 4th December 2009 Frascati, Italy
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Conclusions The ground velocities could be estimated mainly along the coast (urban areas) The vertical velocities indicate that Sicily is uplifting w.r.t. Calabria Good agreement between SAR and GPS East velocities Interseismic deformation is justified by deep slip (below 9 km) on a fault with different geometry than the 1908 modeled source. On the other hand, modeling the 1908 co-seismic displacements using the geometry of the interseismic source, degrades the model fit only slightly (RMS of residuals increases from 3 to 5 cm). To improve our interseismic model, we need more data to better constrain the actual mechanism of strain accumulation Advances in the Science and Applications of SAR Interferometry ESA ESRIN, 30th November - 4th December 2009 Frascati, Italy
Interseismic for the coseismic source
Coseismic model from interseismic parameters
Coseismic model from leveling data
Interseismic model from SAR data
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Up Component Profile 1 - Up Component
E
4 3 2 1 0 -1 -2 -3 -4
250 Elevation (meters)
Ground Velocity (mm/yr)
W
200 150 100 50 0 0
1200
2400
3600
4800
6000
7200
8400
9600
10800
Distance, m
E
Groubd Velocity (mm/yr)
3.0 2.0 1.0 0.0 -1.0 -2.0 -3.0 0
1200
2400
3600
4800
6000
7200
8400
9600
10800 12000 13200
180 160 140 120 100 80 60 40 20 0
Elevation (meters)
Profile 2 - Up Component
W
14400 15600
Distance, m
Profile 4 - Up Component
SE
5.0 4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 -3.0 -4.0
200 180 160 140 120 100 80 60 40 20 0 0
2400
4800
7200
9600
12000
Elevation (meters)
Ground Velocity (mm/yr)
NW
NW
SE
200 150
0
100 -5
50
-10
Elevation (meters)
Profile 3 - Up Component
Ground Velocity (mm/yr)
5
0 0
1600
3200
4800
6400
Distance, m
14400
Distance, Advances in the Science andm Applications of SAR Interferometry ESA ESRIN, 30th November - 4th December 2009 Frascati, Italy
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Descending processing problem D
C
B D
C
A B
A
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Time Series examples Descending dataset
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GPS North
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Interseismic 2D deformation modeling Descending observed velocity
Descending modeled velocity
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