Evidence for crustal low shear-wave speed in western Saudi Arabia from multi-scale fundamental-mode Rayleigh-wave group-velocity tomography

We investigate the crustal and upper-mantle shear-velocity structure of Saudi Arabia by fundamental-mode Rayleigh-wave group-velocity tomography and shear-wave velocity inversion. The seismic dataset is compiled using ∼140 stations of the Saudi National Seismic Network (SNSN) operated by the Saudi Geological Survey (SGS). We measure Rayleigh-wave group-velocities at periods of 8–40 s from regional earthquakes. After obtaining 1-D shear-wave velocity models by inverting group-velocities at each grid node, we construct a 3-D shear-velocity model for Saudi Arabia and adjacent regions by interpolating the 1-D models. Our 3-D model indicates significant lateral variations in crustal and lithospheric thickness, as well as in the shear-wave velocity over the study region. In particular, we identify zones of reduced shear-wave speed at crustal levels beneath the Cenozoic volcanic fields in the Arabian Shield. The inferred reductions of 2–5% in shear-wave speed may be interpreted as possibly indicating the presence of partial melts. However, their precise origin we can only speculate about. Our study also reveals an upper-mantle low velocity zone (LVZ) below the Arabian Shield, supporting the model of lateral mantle flow from the Afar plume. Further geophysical experiments are needed to confirm (or refute) the hypothesis that partial melts may exist below the Cenozoic volcanism in western Saudi Arabia, and to build a comprehensive geodynamic–geological model for the evolution and present state of the lithosphere of the Arabian Plate and the Red Sea.

Citation

Tang Z, Mai PM, Chang S-J, Zahran H (2018) Evidence for crustal low shear-wave speed in western Saudi Arabia from multi-scale fundamental-mode Rayleigh-wave group-velocity tomography. Earth and Planetary Science Letters 495: 24–37. Available: http://dx.doi.org/10.1016/j.epsl.2018.05.011.

Acknowledgements

We thank Dr. Mahmoud Salam, Wael Raddidi, and the entire team at the National Center for Earthquakes and Volcanoes (NCEV) at the Saudi Geological Survey (SGS) for providing the broadband seismic data. We also thank Mohammed Soliman and two anonymous reviewers for their constructive comments that help greatly to improve the manuscript. We acknowledge support by Kangwon National University (KNU) for hosting Z.T. during a research collaboration visit in September 2015. The research presented in this paper was supported by funding from King Abdullah University of Science and Technology (KAUST), grant number BAS/1/1339-01-01. S.-J.C. was supported by the Korea Meteorological Administration Research and Development Program under grant KMIPA 2015-7030.