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