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Seismic risks assessment around the Mediterranean region
Dr. Ferdaous CHAABANE (presenter), Alexis Rigo (Project PI), Martinez-Diaz José, Dr. Tahayt Abdelilah, Briole Pierre, Mourabit
Taoufik, Bezzeghoud Mourad.
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United Nations-Russian Federation Workshop on the Applications of Global Navigation Satellite Systems
Krasnoyarsk, Russian Federation 18 - 22 May 2015
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Issues – The majority of the western Mediterranean regions are
located on a seismic line which exposes them to an increased risk of earthquakes (Africa/Eurasia plates convergence).
– Many geodynamic models were proposed ?! – Poor GPS stations cover. – Many archive data to analyze, how?
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Past Major Earthquakes
Past Major Earthquakes
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• to focalize on ground surface tectonic deformation related to the seismic activity
• Geodynamic deformation understanding ⇒ Early warning is the way to avoid or minimize damages and help concerned countries to evaluate the risks
• Need to combine different types of data.
Objectives
GPS data Satellite images Seismic data
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Outline
• Proposed methodology • INSAR processing • GPS processing • Seismic data exploitation • Resulted deformation model
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Proposed methodology
GPS data Satellite images
Data fusion
Seismic data
A priori information Previous researches
Improved Deformation
model
End User
Data processing Data processing
Deformation model
Deformation model
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INSAR processing
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InSAR principle (1/2)
DTM ou Radar Image3 Radar Image2 Radar image1
différential interferogram
Baseline
DTM © CNES Deformation © CNES
interferogram
© esa
Phase
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Radar Image2 Radar Image1 Radar ImageN DTM
Interferometry & differential interferometry
Data base of several interferograms
InSAR principle (2/2)
Topographic mapping and ground deformation monitoring
Optical Data
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INSAR processing strategy
Four steps: - Choice of the priority targets
- Acquisition of the images and formation of a data base
- Development of new techniques for ground deformation measurements
- Starting of geological interpretations and numerical modelling.
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Pilot sites
Pilot sites
TÉTOUAN'
AL'HOCEIMA'
LORCA'
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INSAR database
• Satellite images data base : ESA Category1 project ⇒ All the archive data (ERS1-2, ENVISAT): about 200 images for the 3 areas of study
• Al Hoceima 37 ENVISAT + 24 ERS • Lorca 36 ENVISAT + 24 ERS • Tétouan 35 ENVISAT + 45 ERS
• Development of a Virtual Machine to facilitate the exploitation of the developed interferometric tools
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INSAR results (1/2)
• Case of Al Hoceima pilot site : 31 differential interferograms has been generated (baseline<150m)
• Interferometric processing: filtering (spatial and temporal), atmospheric correction, unwrapping, etc.
INSAR analysis ⇒ Maximum of information about the deformation model
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INSAR results (2/2)
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GPS processing
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GPS networks data will be collected as far as their temporal compatibilities ⇒ initiate a coordination of measurements of these networks in a joint way.
- Installation of additional permanent GPS stations in Morroco
- Apply processing and monitoring of permanent GPS stations covering all the region of study.
GPS processing strategy
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GPS network densification
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General information for the Iberia-Africa region
Seismicity is broadly distributed over �300 km and earthquakes are of moderate to low magnitude and mostly occur at shallow depths
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New GPS constraints along Africa-Iberia boundary
• To investigate present day deformation
• To estimate the geometry and rates of strain accumulation
• To determine a new velocity field across the most western part of the Africa-Iberia plate boundary,
⇒Rigorous GPS Modeling Combined with Kinematic block modeling
Data • GPS observations : 65 permanent stations, 31 survey-mode GPS sites,
new continuous stations in Morocco and southern Spain.
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GPS observations
• GPS three steps approach:
– GPS phase observations ⇒ to estimate daily positions using loose a priori constraints
– Combine daily positions with similar solutions for over 200 global GPS stations
– Combine all the data in a single solution ⇒ estimate positions, velocities, etc.
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GPS results
GPS / Kinematic block modeling results - The GPS velocity
field shows south-west motion of the central part of the Rif Mountains in north Morocco /Africa (3.5-4.0 mm/yr)
- The Betic Mountains of south Spain move west–southwest/ Eurasia (�2–3 mm/yr)
- GPS velocities for stations in the southwest Betics and in Central Rif show a clockwise rotation
GPS Results
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Seismic data exploitation
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Seismic processing strategy
- Data is analyzed in order to improve : - Precise details of locations, - Focal mechanisms, - Fault characterization, - The crustal structure, etc.
- Analyze seismicity of the zone of study according to the results obtained in geodesy.
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Seismic investigations
Case of Al Hoceima pilot site: • Previous seismological works: similar focal mechanisms and
parallel faults for the two Al Hoceima main shocks: not agree with GPS and InSAR results.
• Inversions of P and SH waveforms were carried out from a dozen teleseismic stations to determine the detailed rupture history for the two main shocks
• Twenty autonomous seismological stations were deployed during two weeks following the main shocks in the epicentral zone of Al Hoceima => Aftershock magnitudes
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Seismic investigations
• Bars are the two modeled faults (GPS/INSAR).
• Rectangle:the cross-section frame.
• picA, picB and picC-D indicate location of ground photographs.
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INSAR, GPS and Seismic data analysis Deformation modeling
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Data diversity
• Red ellipse delimits the damaged area.
• Stars show the epicenter locations of the Al Hoceima main shock with corresponding focal mechanisms estimated by different data centers.
• Blue rectangles denote subsets of ENVISAT ASAR images
• Red triangles are GPS stations : MDAR and BBFH have GPS measurements of coseismic displacements included in the modeling.
• Yellow triangles represent seismic temporary array stations used to collect
• Rectangle oriented E-W delimits the area covered by the showed interferograms
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Deformation model (1/2)
To fit the available observations, we suggest a model with two abutting, conjugate faults
The result of a comprehensive modelling procedure considering quantitative and qualitative contributions from InSAR/GPS/seismological information
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Deformation model (2/2)
Arrows indicate the relative movements of these blocks with respect to the Africa plate.
Tectonic interpretation of the cross-fault model inferred in this study
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Conclusion and perspectives
- Western Mediterranean = scientific and educational challenge for the next 10 years
- GPS data + satellite imagery + seismic data combination ⇒
Geodynamic comprehension and tectonic risk - establishing a long-term Mediterranean partnership with
common scientific objectives and exchanges of ideas
- Allowing all the countries to benefit of the recent spatial imageries and processing developments
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Thank you for your attention