Discriminating Lithospheric and Asthenospheric Anisotropy Beneath Northern Oman: Sharp Contrast Observed at the Semail Gap Fault Zone

• Published in: Journal of geophysical research. Solid earth Vol. 129; no. 6
• Main Authors: Komeazi, A., Kaviani, A., Rümpker, G., Weidle, C., Meier, T.
• Format: Journal Article
• Language: English
• Published: 01.06.2024
• Subjects: lithosphere; northern Oman; obduction; seismic anisotropy; Semail Gap Fault Zone; shear wave splitting
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2023JB028627

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 October 2013. By examining the azimuthal distribution of shear wave splitting (SWS) parameters, we were 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 variations versus back‐azimuth, indicating the potential presence of depth‐dependent anisotropy. The General NW‐SE trend of the Fast Polarization Directions (FPDs) of the one‐layer anisotropy in the west and FPDs of the upper layers in the east is concordant with the strike of the structures resulting from the collision between the continental and oceanic plates. A clear contrast in SWS parameters is observed in the Semail Gap Fault Zone (SGFZ), suggesting that the SGFZ can be a lithospheric‐scale structure that hampers the intrusion of mafic magma from the southeast. Furthermore, the FPDs of the lower layer in the east exhibit an NE‐SW trend, which may be indicative of the large‐scale mantle flow resulting from the present‐day plate motion. Plain Language Summary In this study, we investigated how the lithosphere beneath northern Oman is deformed by using shear wave splitting (SWS) analysis. We used a dense network of 58 seismic stations, including both permanent and temporary stations. Based on our shear wave splitting observations the region can be divided into three parts. In the west, the splitting parameters (delay time and fast polarization direction) are generally consistent, which is in good agreement with the rigid continental lithosphere, suggesting a single anisotropic layer. In the central and eastern regions, the splitting parameters show different behaviors, indicating more complex and depth‐dependent structures. The Semail Gap Fault Zone (SGFZ) marked a significant boundary in SWS parameters, which represent the SGFZ as a geological boundary. Additionally, NE‐SW FPDs indicate large‐scale mantle flow due to present‐day plate motion. Key Points A sharp contrast in shear wave splitting parameters is observed at the Semail Gap Fault Zone Indications for depth‐dependent anisotropy are observed in the eastern part of Northern Oman Regional variances in anisotropic pattern indicate lateral variation in lithospheric structure