Present-day deformation rates across Oman based on space Geodesy

Oman is situated in the southeastern Arabian plate, just behind the Makran subduction zone. The internal stability of this portion of the Arabian plate must be questioned, however, based on recent studies focusing on long-term observations. These studies provide evidence of active deformation in the Hajar mountains of northern Oman and the UAE. Specifically, recent studies that focused on vertical deformation, yielded temporally and spatially variable vertical rates ranging from 0.01 to 0.89 mm/a in northeastern region of the Arabian Peninsula (Hoffman et al., 2020). Others presented evidence of the continuing uplift of some domes in the Hajar mountains. Furthermore, a significant seismic contrast is well-documented along the Makran subduction zone in Iran and Pakistan. This provides an opportunity to study whether the regional-scale uplift pattern of the Hajar mountains correlates with the variability in deformation style along the Makran plate interface or is caused by driving forces unrelated to horizontal plate motion and subduction. Monitoring the contemporary motions of the northeastern boundary of the Arabian plate can, therefore, enhance our understanding of the complex kinematics of the Makran region. Here, we provide first results of our space-geodetic study in which we combine, both, vertical and horizontal motion analysis to determine the present-day 4D-temporal and spatial strain variability across Oman.

The National Survey Authority (NSA) that runs the GNSS reference network across the Sultanate of Oman, established a continuously operating network of 47 sites in 2016. Since its establishment, the network served numerous positioning and mapping activities within the country, providing a precise tool to study the internal deformation of the southeastern Arabian plate. Six-and-a-half years of continuous data acquisition were utilized in our study, combined with 26 IGS stations, to derive horizontal and vertical displacement rates, initially in ITRF20.

A new regional reference frame for Oman was realized by rotating ITRF20 so that the horizontal velocities of the Oman CORS stations are minimized in the new reference frame ONGD23. As a result of this process, the average rigid-body rotation of the Arabian plate was estimated and eliminated. The residual velocities illustrate internal horizontal and vertical deformation across Oman, ranging from fractions of millimeters per year to a few millimeters per year. The spatial pattern varies from 1.5 mm/a subsidence in the north to 0.1 mm/a uplift in the northeast. Subsidence of 1.2 to 1.8 mm/a is documented around oil fields. The results also yield uplift rates of up to 0.8 mm/a near certain domes of the Hajar mountains. A noticeable pattern of subsidence transitioning to uplift, from west to east, is observed across the Hajar mountains. Surprisingly, however, the southern flanks of the mountains yield gradual uplift rates. The Arabia – Eurasia plate convergence cannot be directly responsible for such regional scale uplift. Additional mechanisms must be invoked to explain this enigmatic intra-plate strain.