Refined models of gravitational potential energy compared with stress and strain rate patterns in Iberia |
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| Institution: | 1. Centre d''Estudis de la Neu i de la Muntanya d''Andorra, Institut d''Estudis Andorrans, Andorra;2. Departamento de Petrología y Geoquímica, Universidad Complutense de Madrid, 28040 Madrid, Spain;3. Departament de Geodinàmica i Geofísica-Institut de Recerca GEOMODELS, Universitat de Barcelona (UB), Martí i Franquès s/n, Barcelona 08028, Spain;4. Departament de Geoquímica, Petrologia i Prospecció Geològica, Universitat de Barcelona (UB), Martí i Franquès s/n, Barcelona 08028, Spain;5. Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Sektion Geochronologie, Königsbrücker Landstraße 159, D-01109 Dresden, Germany;1. Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Japan;2. Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, Japan;3. Earthquake and Volcano Observatory, Graduate School of Science and Technology, Hirosaki University, Japan;4. Disaster Mitigation Research Center, Nagoya University, Japan;5. Research Center of Earthquake and Volcanoes, Graduate School of Environmental Studies, Nagoya University, Japan |
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| Abstract: | This study examines the role of gravitational potential energy (GPE) in generating second-order (spatial scale ∼102 km) variations in the Iberia stress and strain-rate patterns. We present a new map of present-day strain rate field derived from the secular velocity field computed using all available continuously operating Global Navigation Satellite Systems (GNSS) stations in Iberia. The estimated strain rate field is generally consistent with the tectonic framework of the Iberian region, even though sporadic sharp local variations downgrade its correlation with the regional stress patterns. Many of the sharp spatial variations in the strain rate map are consistent with local changes of deformation style determined by prevailing faults. To obtain a more accurate estimate of GPE we use new data on the structure of the crust and apply a thin sheet approach using a 3-D definition of deviatoric stress. The GPE is derived from two isostatically compensated models (GPEd and GPEe compensated by density and elevation adjustment, respectively) and from the truncated geoid (GPEg). The GPE stresses are then summed with the first-order stress field due to the Eurasia–Nubia (EU–NU) convergence and the results compared with both the stress and strain rate data. In agreement with previous studies, we find that the GPE does not significantly change the NW–SE average direction of the most compressive stress (SHmax) imposed by the EU–NU collision, its main effect being to cause spatially changing stress regimes. From the analysis of the different GPE models we find: (1) in the Pyrenees, the tectonic forces have a secondary role when compared to the GPE. In this region, the model that best correlates with observations is the one emphasizing the role of surface elevation as a source of GPE (GPEe); (2) in the Iberian Chain and the Betics, the GPE imposes NE–SW extension consistent with a strike-slip regime and is equally (GPEe) or more (GPEg) important than the tectonic forces. In these regions, both deep heterogeneities associated with mantle convection and elevation are important sources of GPE; (3) in western Iberia, the GPE differences work against dominant tectonic forces by reducing the SHmax magnitude. The GPEg model is the one that best predicts the average strike-slip regime in Galicia; and finally (4) in the Gulf of Cadiz the gravitational potential stresses have a minor role and the style of deformation is clearly controlled by the tectonic forces. |
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| Keywords: | Gravitational potential energy Iberia Plate tectonics Stress field Strain rate |
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