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Revista Geológica de América Central ISSN: 0256-7024 [email protected] Universidad de Costa Rica Costa Rica Lücke, Oscar H. STATE OF STATIC STRESS ON THE COSTA RICAN COCOS-CARIBBEAN PLATE INTERFACE: MECHANICAL INTERPRETATION FOR THE ORIGIN OF ASPERITIES ON THE SEISMOGENIC ZONE Revista Geológica de América Central, núm. 53, julio-diciembre, 2015, pp. 75-88 Universidad de Costa Rica San José, Costa Rica Available in: http://www.redalyc.org/articulo.oa?id=45442429006 Abstract The forearc region along the Central American Subduction Zone shows a series of trench-parallel posi-tive gravity anomalies with corresponding gravity lows along the trench and toward the coast. These features extendfrom Guatemala to northern Nicaragua. However, the Costa Rican section of the forearc does not follow this patterndue to the segmentation of the along-trench gravity low, the absence of the coastal low, and the presence of emergedcontinental mass along the forearc gravity high at the Nicoya Peninsula. Geodetic and seismological studies along theCosta Rican Subduction Zone suggest the presence of coupled areas in the seismogenic zone beneath the Nicoya Pe-ninsula prior to the 7.6 Mw magnitude earthquake of September 5th, 2012. These areas have previously been associatedwith asperities. Based on the structure of the overriding plate, former publications have proposed a mechanical modelfor the origin of asperities along the Chilean convergent margin, in which the dense igneous material in the forearc ofthe overriding plate above the seismogenic zone modifies/disturbs the state of static stress and influences seismogenicprocesses. In Costa Rica, surface geology and gravity data indicate the existence of dense basalt/gabbro crust overlyingthe seismogenic zone where the coupling is present. Bouguer anomaly values in this region reach up to 120×105m/s2and are the highest for Costa Rica. In this research, the state of static stress on the Cocos-Caribbean plate interface iscalculated based on the geometry and on the density distribution of a 3D litosphere density model of the subductionzone as interpreted from gravity data from combined geopotential models. Results show a spatial correlation betweenthe coupled areas at the Nicoya Peninsula and the presence of anomalies on the static state of stress on the plate inter-face. The stress anomalies were calculated for the normal component of the vertical stress on the seismogenic zone andwere interpreted as being generated by the dense material which makes up the forearc in the area. The dense material of the Nicoya Complex mafic rocks and the topographic load of the peninsula on the seismogenic zone lay a role in thedistribution of coupled areas and the seismic behavior of the region, since the anomalies on the normal stress on theplate interface may increase the shear stress threshold to generate the rupture. Keywords Tectonic stress, asperities, seismogenesis, geophysics, gravimetry. How to cite Complete issue More information about this article Journal's homepage in redalyc.org Scientific Information System Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Non-profit academic project, developed under the open access initiative
