Coupled Geodynamic and Seismological Modeling

The interpretation of isotropic and anisotropic seismic data in terms of tectonic plates and mantle dynamics is generally difficult and non-unique. Geodynamic modeling can provide insights into the nature of the seismic data by reproducing the macro- and micro-flow processes that control the evolution of different tectonic settings and their seismological (elastic) properties.

This type of coupled modelling is based on 3 different numerical simulations (Fig. 1):

1) macro-flow simulations reproduce the large scale evolution of a given tectonic setting.

2) micro-flow simulations predict the strain-induced fabric evolution of deformed rocks (which may cause seismic anisotropy) according to the macro-flow velocity gradient field. Additional complexities such as preexisting fabrics, compositional layering or fluid/melt-filled cracks can also be included.

3) seismological synthetic experiments.

Figure 1 - Synopsis of the numerical workflow.

The numerical techniques are explained in a series of articles (Faccenda and Capitanio, 2012 and 2013; Faccenda, 2014) in which, together with several colleagues (geodynamicists and seismologists), the potentialities of this method have been tested in both generic models of mantle convection (near convergent margins) and models aiming to reproduce the evolution of real tectonic settings (such as the Tonga-Kermadec subduction zone).

Another useful application of this method is represented by the possibility of testing and improving the robustness of seismological inversion experiments, such as teleseismic P-wave tomography (Fig. 2).

Figure 2 - Results of inverting P-wave synthetic data in a geodynamic model of subduction zone. Panels A, C and E show horizontal slices at 195 km depth. Panels B, D and F show vertical cross-sections at 0.25 °S. The left, central and right columns were produced, respectively, from isotropic, total travel-time and total-travel-time data with a-priori information about seismic anisotropy. In all cases the inversion assumes isotropic velocities. Note the appearance of artificial low velocity anomalies in the inversion of anisotropic data (C-D), which vanish when a-priori constraints about the anisotropy field are used (E-F). Dashed lines show isovelocity contours from the input model.

From (Bezada et al., 2016, Gcubed)

Publications:

1. Bezada M., Faccenda M., Toomey D. R. Representing anisotropic subduction zones with isotropic velocity models: A characterization of the problem and some steps on a possible path forward. Geochem. Geophys. Geosyst., doi:10.1002/2016GC006507 (2016).
2. Chang S.-J., Ferreira A.M.G., Faccenda M. Upper-and mid-mantle interaction between the Samoan plume and the Tonga-Kermadec slabs. Nat. Commun. 7:10799, doi: 10.1038/ncomms10799 (2016).
3. Faccenda M. Mid mantle seismic anisotropy around subduction zones. Phys. Earth Planet. Int. 227, 1-19 (2014).
4. Faccenda M. and Capitanio F. A. Seismic anisotropy around subduction zones: insights from three-dimensional modeling of upper mantle deformation and SKS splitting calculations. Geochem. Geophys. Geosyst., doi:10.1002/ggge.20055 (2013).
5. Faccenda M. and Capitanio F. A. Development of mantle seismic anisotropy during subduction-induced 3D flow. Geophys. Res. Lett. 39, doi:10.1029/2012GL051988 (2012).
6. Faccenda M., Burlini L., Gerya T.V., Mainprice D. Fault-induced seismic anisotropy by hydration in subducting oceanic plates. Nature 455, 1097-1100 (2008).