Discriminating lithospheric and asthenospheric anisotropy beneath Northern Oman: sharp contrast observed at the Semail Gap Fault Zone

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To gain a deeper understanding of the extensive and varied lithospheric deformations beneath northern Oman, we examine seismic anisotropy in this region using splitting analysis of teleseismic shear wave data. Our study utilizes data from a dense network consisting of 13 permanent and 45 temporary seismic stations, which were operational for approximately 2.5 years starting from 2013. By examining the azimuthal distribution of shear wave splitting (SWS) parameters, we are able to divide the study area into three sub-regions. The stations located to the west of the Hawasina window exhibit relatively azimuthally invariant SWS parameters suggesting a single anisotropic layer. On the other hand, most of the stations located in the central and eastern regions display a 90-degree periodicity versus back-azimuth, indicating the presence of depth-dependent anisotropy. The General NW-SE trend of the Fast Polarization Directions (FPDs), one-layer/upper layer FPDs in the east and one-layer FPDs in the west, is concordant with the strike of the structures resulting from the collision between the continental and oceanic plates. Notably, a distinct contrast in the SWS parameters is observed at Semail Gap Fault Zone (SGFZ), suggesting that the SGFZ can be a geological border for the mafic intrusive emplacement from the east. Furthermore, the fast axes of the lower layer exhibit an NE-SW trend, which may be indicative of the large-scale mantle flow resulting from the present-day plate motion.

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