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Project LTV-SourceMod4PSHA Versão para impressão

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LTV-SourceMod4PSHA Construction of a seismic source model for the Lower Tagus Valley to use in future probabilistic seismic hazard assessment Leader: CGE, Coordinator: Delphine Fitzenz
Funding: Fundação para a Ciencia e a Tecnologia
Budget: 110 k€
Start date: April 2010
Duration: 3 years

 

 

Abstract

When aiming for the probabilistic earthquake hazard assessment for a given region, one has to study the sources of the seismic waves which might cause damage, their propagation through the earth, and their potential amplification at the sites of interest. This project focuses on the first aspect: the construction and the evaluation of models for the seismic sources relevant for the Lower Tagus Valley (LTV). It is well known that large earthquakes happened in the past on the SW margin of Portugal and were strongly felt in Lisbon and in its surrounding region (in 1755, moment magnitude Mw ~8.5) and on Feb. 28 1969, Mw=7.3). However, large events can also initiate in the LTV itself, as shown by the historical accounts for magnitude 6 to 7 earthquakes in 1344, 1531, and 1909 for example (Martins01). Geophysically-determined fault offsets also point to the recurrence of Mw 6 earthquakes every few thousands of years close to Porto Alto and Vila Franca de Xira (CarvalhoJ06). Because of the short distances within the LTV, a point-source approximation for the ruptures will not be a valuable first order approximation. On the contrary, information on the lateral extension of faults or seismic source zones will be essential.
The challenges will therefore be to collect, combine, and possibly complement information of various types: the historical and instrumental earthquake catalogues, mapped active faults, geophysical subsurface data on fault geometry and offsets, and paleoseismological information as they become available. A probabilistic modelling framework will be designed and used to 1) study the correspondence between faults and earthquakes following Wesson03, and 2) to test the pertinence of different ways of characterizing the sources (faults, diffuse zones, etc.) in terms of the robustness of the resulting hazard maps (i.e., maps of expected ground shaking level for given return periods). Such sensitivity analyses were performed by Beauv06a,b. To compute hazard maps, we will use a simplification of the propagation and amplification processes in the form of ground motion prediction models designed for finite faults (see Abrahamson08). Using 3D wave propagation through a 3D velocity structure (Grandin07) will become important when the actual hazard maps are computed but it is beyond the scope of this proposed project. Direct numerical fault modelling will also be instrumental in 1) studying the geometry of the faults and the tectonic regimes with respect to the boundary conditions on the region (indeed, discrepancies in the numerical models might indicate where probable, yet unknown faults might lie, (Fitzenz04), and 2) propose physics-based renewal models for characteristic strong earthquakes (Fitzenz07).
One expected outcome of the project will be a list of recommendations pertaining to the data most needed to complement the results of this project and achieve a robust, consistent source model for use in the next generation of probabilistic earthquake hazard assessment in the Lower Tagus Valley.
The team members have knowledge and skills in seismology, wave propagation, seismic source characterization (using geophysics, seismology, geomorphology, and paleoseismology), as well as in numerical deterministic and probabilistic modelling. Current projects of the Seismolitos group of the CGE are already focused on the Lower Tagus Valley in the framework of FCT projects (PTDC/CTE-GIN/82704/2006), and are studying the propagation aspects. This proposed project will provide direct input to SISMOD/LISMOT (Finite Seismic Source Modeling by Joint Inversion of Seismic and Geodesic Data and Strong ground motion in the Lower Tagus Valley).

 

Participants

Delphine Fitzenz, CGE, University of Evora
André Jalobeanu, CGE, University of Evora
José Fernando Borges, CGE, University of Evora
Matthieu Alexis Ferry, CGE, University of Evora
Mourad Bezzeghoud, CGE, University of Evora
Céline Beauval, LGIT/IRD, Grenoble, France
Frantz Maerten, IGEOSS, Montpellier, France

Boris Le Goff, PhD student, University of Evora
Rafaela Chumbo, MSc student, University of Evora

 

Job Openings

We propose a research grant for 6 months or more, to work on the historical seismicity of sources within and around the Lower Tagus Valley (starting date May 2010 or until the position is filled). For this kind of tasks, earthquake geology, history, and studies on the cohesion of the social network as well as the stability of structures and buildings are equally important. The grant is open for MSc students or MSc holders. Since the work will include looking at archives, and working with schools, a good knowledge of Portuguese is required.

We will also look for possibly up to 2 other students to work on different aspects of the modeling work (both on the mechanics side and on the hazard map side). Possibilities for funding are being explored. If you are interested, please contact us!

As usual with the FCT, interested candidates for PhD and postdocs grants can also contact us to build a strong application file for the individual call for proposals . Since the work would be done in the framework of a funded and well evaluated project (91/100), an application would have good chances of being accepted. Next deadlines for these individual fellowships: September 6, 2010. For more information on the grants and the application procedure, go to the FCT page.

 

Tasks and Milestones of the project

Project Flowchart
Ficheiro:LTV SourceMod4PSHA1.pdf
Project Timeline
Ficheiro:SourceModTimeline.pdf
Full Project (file generated by the FCT following the project submission)
Ficheiro:SourceModoverview.pdf

 

Outreach project

We have proposed to schools of the Lower Tagus Valley to participate in an Outreach project.
Students who are not part of the participating schools but would like to contribute can find details and questionnaires at the dedicated web site.
The organizing team includes Prof. Mourad Bezzeghoud, Dr Delphine Fitzenz, and Rafaela Chumbo.