Costa Rica Stress Map: the Sigma ProjectCosta Rica Stress Map: the Sigma Project

Allan López , Jeffrey S. Marshall , Ana Leyla Chinchilla , Peter B. Sak , Sergio Chiesa , Martin Meschede ,Guillermo E. Alvarado , Esteban Gazel , Adrian Villegas ,

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Instituto Costarricense de ElectricidadUniversidad Latina de Costa Rica

Cal Poly Pomona University, U.S.A.Private Consultant, Germany

Dickinson College, U.S.A.University of Bergamo, Italy

Universität Greifswald, GermanyUniversidad de Costa RicaRutgers University, U.S.A.

Consultor Privado, Costa Rica

Miocene to Quaternary fault-slip populations, dike orientations, borehole breakouts, cinder cone alignments, and earthquake focalmechanisms covering 60% of Costa Rica are compiled and analyzed to obtain an updated and more realistic reconstruction of the evolutionand partitioning of the paleo- and modern stress field in this region of southern CentralAmerica.

In general, the trend of present day Maximun horizontal Stress (SHmax) depicts an average orientation of N22 ºE, similar to the N30ºEconvergence direction between the Cocos and Caribbean plates. The Cocos plate subducts beneath the Caribbean plate along the MiddleAmerica Trench at a rate of 75-90 mm yr . This plate convergence constitutes the primary control on both modern and past deformation inthis region.

Stress partitioning is recognized within several sub-domains, as well as important deflections in the vicinity of major regional structures,cordilleras, and tectonic blocks.At these locations the contraction is mainly N-S and N33ºW, while transtension (rather than pure distension)is presently acting within the neovolcanic sub-domains. Recent clockwise SHmax rotation from NW to NE is also postulated, reflectingrelative plate displacements.

For the first time it is possible to detect and map subtle changes between the local and regional stress fields allowing for direct application inresearch on seismic hazards, tectonic modeling, and design of civil engineering works. An expanded version of the Sigma Project coveringall of CentralAmerica is likely in the near future as a contribution to the World Stress Map Project (WSMP).

Our special aknowledgements to Damien Delvaux (RoyalAfrica Museum,Belgium) & Oliver Heidbach (WSM Team, Germany) for their kind assistance

Michael Calderón , Rafael Barquero8

Chopo

Reventazon

Tivives

Upala

Pirris Gal 3

Boruca

-87º00 -84º00

7º 00 7º 00

10º 30 10º 30

Projection: Lambert_Azimuthal_Equal-Area

World Stress Map Rel. 2008Heidelberg Academy of Sciences and Humanities

Geophysical Institute, University of Karlsruhe

Applications :

Basin modelling

Tectonic modelling

Reservoir management

Stability of mines, tunnels and boreholes

Fault-slip tendency

Seismic risk assessment

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SH from focal mechanisms

SH from mesoscale faults

SH from Breakouts & Quaternary volcanicalignments and dikes

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