FFRIC fault friction coefficient. vbcAL magnitude of west-directed surface velocity imposed in some AL nodes. TAUMAX maximum down-dip integral of shear ...
Gravitational potential energy and the forces driving plate motions in Iberia M.C. Neves1,6, M. Neres2,6, R. Fernandes3,6, L. Matias4,6, M.M.C. Carafa5 1 Universidade do Algarve, Faro, Portugal 2 Instituto Português do Mar e da Atmosfera, Portugal 3 University of Beira Interior, Covilhã, Portugal 4 University of Lisbon, Lisboa, Portugal 5 Instituto Nazionale di Geofisica e Vulcanologia, Italia
6 Instituto Dom Luiz, Lisboa, Portugal
Tectonic setting
Stress data
Custódio et al., 2015
Topography / SHmax trajectories
Regional stress patterns
GPS strain rate
Seismic strain rate
1st GPE models
Predicted stress
Isostatic compensation Density
Elevation
Neves et al., 2014
Neotectonic FEM model
Neres et al., 2016
Inputs
Modeled plates AF EU AL
Africa (Nubia) Eurasia Alboran
Model parameters FFRIC fault friction coefficient vbcAL magnitude of west-directed surface velocity imposed in some AL nodes TAUMAX maximum down-dip integral of shear traction in the AL subduction shear zone trmxPL maximum shear tractions allowed under plate PL FEG finite element grid Geodynamic scenarios poleBC angular velocity model, defined by an Euler rotation pole 2plates plate configuration model including AF and EU plates 3plates plate configuration model including AF, EU and AL plates geodetically-defined poleBC (Fernandes et al , 2003; 2013) SEGAL2013 geologically-defined poleBC (DeMets et al , 2011) MORVEL Scored regions ALL RoI
all modeled region (FEG area) region of interest: zoom into the Gulf of Cadiz and Alboran region
Datasets
Stress indicators
GPS velocities
Interpolated stress indicators
SCORING OF MODELS
BEST neotectonic MODEL
Velocity field
Fault activity
SHmax
GPE only
Best (TOTAL)
Relative contributions of GPE and Plate boundary forces
Strain rate
GPE only
Best (TOTAL)
Relative contributions of GPE and Plate boundary forces
Conclusions The combination of GPE and plate tectonic forces is sufficient to explain the first and secondorder features of the observed stress field in Iberia.
The GPE creates stresses that compete with the stresses induced by plate tectonic edge forces. The GPE does not significantly change the average direction of the most compressive stress (NW–SE) imposed by the EU–NU collision, a fact explaining why the best model predictions are consistently found near the plate boundary (Gulf of Cadiz, Iberian Chain and Betics). However, it changes the relative magnitudes of the stress tensor components, so we conclude that the main effect of the GPE in Iberia is to induce spatially changing stress regimes. The most significant effect of GPE occurs: • In the Pyrenees, where the GPE accounts for the existence of an extensional regime. • In the Iberianv Chain and eastern Betics, where it imposes NE–SW extension consistent with a strike-slip regime.
References Neres, M., Carafa, M.M.C., Fernandes, R., Matias, L., Duarte, J.C., Barba, S., Terrinha. P., 2016. Lithospheric deformation in the Africa–Iberia Plate Boundary: improved neotectonic modeling testing a basal-driven Alboran plate. J. Geophys. Res. (submitted)
Custódio, S., Dias, N.A., Carrilho, F., Góngora, E., Rio, I., Marreiros, C., Morais, I., Alves, P., Matias, L., 2015. Earthquakes in Western Iberia: improving the understanding of lithospheric deformation in a slowly deforming region. Geophys. J. Int. http://dx.doi.org/ 10.1093/gji/ggv285. Neves, M.C., Fernandes, R.M., Adam, C., 2014. Refined models of gravitational potential energy compared with stress and strain rate patterns in Iberia. J. Geodyn. 81, 91–104. http://dx.doi.org/10.1016/j.jog.2014.07.010.
