New developments in the analysis of shear-wave splitting with applications to temporary networks in South America, East Africa, and the Middle East
IPGP - Îlot Cuvier
Séminaires de Sismologie
Goethe-Universität Frankfurt am Main
Seismic anisotropy provides a unique link between directly observable surface structures and the more elusive dynamic processes in the mantle below. The ability to discriminate between anisotropic structures at different depth levels is of great significance for the geodynamic interpretation of surface-recorded waveform effects. The classical analysis of SKS-splitting observations has been used very successfully to map lateral variations of anisotropic structures of the lithosphere-asthenosphere system. However, the main shortcoming of this approach is the lack of vertical resolution. Here, I will present recent examples of SKS-splitting observations from the Nazca subduction zone (Wölbern et al. 2014) and the East African rift system (Homuth et al. 2014) and discuss how finite-difference waveform modeling can be used to discriminate between plausible models of anisotropy to constrain the anisotropic fine structure. While waveform modeling can provide some constraints on anisotropic layering, the tradeoff between layer thickness and strength of anisotropy cannot be resolved completely. This may be overcome by the analysis of converted Ps-phases in multi-layered anisotropic media (Rümpker et al. 2014). In (weakly) anisotropic media, Ps-phases exhibit a distinct variation in arrival time as function of back-azimuth. This variation can be exploited by time-shifting and stacking of radial receiver functions to constrain a range of possible splitting parameters for an anisotropic layer. Then, the minimization of the transverse-component energy is used to select the pair of splitting parameters that best describes the anisotropic properties of the layer. This 2-step approach stabilizes the inversion process and significantly reduces the time for computing the best splitting parameters. As an example, the method is applied to data from seismic stations in Iran. References: Homuth, B., Löbl, U., Batte, A., Link, K., Kasereka, C. M., Rümpker, G., 2014. Seismic anisotropy of the lithosphere/asthenosphere system beneath the Rwenzori region of the Albertine Rift, rev. manuscript submitted to Int. J. Earth Sci. Rümpker. G., Kaviani, A., Latifi, K., 2014. Ps-splitting analysis for multi-layered anisotropic media by azimuthal stacking and layer stripping, Geophys. J. Int., in press. Wölbern, I., Löbl, U., Rümpker, G., 2014. Crustal origin of trench-parallel shear-wave fast polarizations in the Central Andes, Earth and Planetary Science Letters, 392, 230-238, http://dx.doi.org/10.1016/j.epsl.2014.02.032.