Gravitational potential energy and the forces driving

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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.