## 3 Interpretation and Discussion  
Depth range: 10-30 km (crust). The parameter \(\xi\) (Table 2) shows higher values for the regions 3, 4 and 5. For the region 3 and 4, the higher values of \(\xi\) agree with the anisotropic perturbation determined for the Mesopotamian Plain by [PERSON] et al. [3]. These higher values of \(\xi\) can be related to the lithospheric level observed beneath the Mesopotamian Plain ([12; 13; 14]) and can be also related to the vertical alignment of minerals in the crust due to its horizontal shortening [3], caused by the collision between the Arabian and Eurasian plates from -14 Ma, which has originated a horizontal lithospheric shortening of the Arabian platform, the Mesopotamian Plain and the Zagros belt. For region 5, the higher values of \(\xi\) can be related to shape-induced anisotropy, which is caused by small-scale isotropic heterogeneities preferentially oriented in a strain field [11], as can occur in folded zones such as the Oman-folded zone (OFZ, Figure 9a). This shape-induced anisotropy can exist for the crust and the subcrustal lithosphere. This kind of anisotropy is obviously difficult to interpret, because it is related to a complex geodynamic development, and the resultant pattern of deformations is also very complex.  
Depth range: 30-100 km (upper mantle). The parameter \(\xi\), (Table 2) shows higher values for the regions 1 (30-100 km-depth), 2 (55-100 km-depth) and 5 (30-100 km-depth). For region 1, the higher values of \(\xi\) can be related to the plume material propagation in the Arabian shield, from the Afar plume ([14; 15; 16; 17; 18; 19; 20; 21]), and to the Yemeni Oligocene Trapps, which was formed by the infiltration of Afar plume material \(\sim\)30 Ma [22], and it may indicate the existence of magmatic underplating at crustal depths [23]. Also, these higher values of \(\xi\) can be related to the post-12 Ma volcanism in western Arabia [17]. For region 2, the higher values of \(\xi\) can be related to mantle plume material from the Jordan plume. [PERSON] and [PERSON] [17] determined a low-velocity anomaly in their model just beneath Jordan and northern Arabia, and they related this anomaly to the Jordan plume, suggesting that this plume may have formed the Syrian volcanic rocks. Also, these higher values of \(\xi\) can be related to the existence of a lithospheric keel, which was observed beneath the Arabian platform and the Taurus-Zagros folded zone (TZFZ) in previous studies ([12; 13; 14]). The fast axes directions of the shear-wave splitting data determined for this region in previous studies ([4; 24; 25; 26; 27; 28]) are interpreted as toroidal flow around a lithospheric keel beneath this region by [PERSON] et al. [27].  
Figure 11: Region 1: (**a**) The SV (blue line) and SH (red line) velocities, determined from anisotropic inversion, are compared with the isotropic S-velocity (black line, Table 1). (**b**) The theoretical Love and Rayleigh phase velocities (continuous line), calculated from the anisotropic model (**(a)**, SV and SH velocities), are compared with the Love and Rayleigh phase velocities as in Figure 10. The vertical and horizontal bars have the same significance as Figure 10.