Shear Velocity Structure Beneath Saudi Arabia From the Joint Inversion of P and S Wave Receiver Functions, and Rayleigh Wave Group Velocity Dispersion Data

Abstract

We develop a new 3-D shear velocity model for the lithosphere and sublithospheric mantle under Saudi Arabia by jointly inverting P wave receiver functions, S wave receiver functions, and fundamental-mode Rayleigh wave group velocities. P and S receiver functions are calculated from earthquakes recorded between 2012 and 2015 at 156 Saudi National Seismic Network stations operated by the Saudi Geological Survey. Rayleigh wave dispersion data are extracted from independent tomographic studies. Our model reveals significant lateral variations in crustal and upper-mantle S velocity below Saudi Arabia. Particularly, a low-velocity zone, with minimum S velocity of~4.0 km/s in the depth range of 70-190 km, is observed under the Arabian Shield coinciding with Cenozoic surface volcanism. The low-velocity zone is found consistent with the presence of partial melts in the mantle and interpreted as a potential deep magma source for the volcanism in western Arabia. We propose that magmas responsible for the Arabian volcanism may be derived from multiple sources. Both lithospheric thinning and the Afar plume trigger magma production beneath southwestern Arabia, while decompression melting caused by the lithospheric thinning may be the main factor in the central and northern portions. Furthermore, we find evidence for localized crustal low shear velocity anomalies (2-4% reductions) that appear spatially correlated to the volcanism; these may be due to fractures caused by magma ascent and small amounts of partial melt in the crust. This spatial distribution of S velocity reductions may indicate the plumbing system for magma ascent underneath western Arabia.

Crustal and uppermost mantle shear wave velocity structure beneath the Middle East from surface wave tomography

“…The sedimentary cover in the Arabian Platform gradually thickens eastward and reaches more than 10 km thickness beneath the Mesopotamian Foredeep and Persian Gulf (Seber 1997). Figures 4, 9 and S11) suggest that on average the Arabian Shield has higher crustal seismic velocities than the Arabian Platform, in agreement with previous studies (Hansen et al, 2007(Hansen et al, , 2008Tang et al, 2016Tang et al, , 2018Tang et al, , 2019. The velocity map at 8-km depth (Figure 4) exhibits high velocities beneath the Arabian Shield and Afar depression where magmatic crystalline rocks are exposed at shallow depths.…”

“…In regions where continuous seismic noise records were not available, such as Saudi Arabia, we incorporated dispersion curve data from previous studies to improve ray coverage. We used the dispersion measurements by Tang et al (2018Tang et al ( , 2019 for Rayleigh waves (periods 8-75s) observed at 143 permanent broadband stations of the Saudi National Seismic Network (SNSN) (green triangles in Figure 2) for regional earthquakes (EQ) located inside our study area. The inclusion of these EQ-based dispersion data dramatically improves the ray coverage across Arabia ( Figure S3).…”

“…Previous seismic imaging studies (e.g. Rodgers et al, 1999;Tkalčić et al, 2006;Park et al, 2007Park et al, , 2008Hansen et al, 2007Hansen et al, , 2008Tang et al, 2016Tang et al, , 2019 suggested that the crust thickens rapidly eastward from less than 25 km beneath the western Arabian Shield and Red Sea to 40-45 km beneath the central region of the Arabian Shield. In contrast, our Vs model reveals a very complex crustal structure beneath the Red Sea and Arabian Shield, so that the Moho can hardly be identified (Figures 9, S11 and S12).…”

“…Numerous regional tomography studies have provided information on upper mantle structures beneath different regions of the Middle East (e.g. Kaviani et al, 2007;Biryol et al, 2011;Salaün et al, 2012;Simmons et al, 2015;Portner et al, 2018;Tang et al, 2016Tang et al, , 2018Tang et al, , 2019. However, because of data access limitations, these studies have often been limited by political boundaries.…”

“…In the past few years, crustal structure has been studied in different parts of the Middle-East region using receiver function analysis and surface-wave tomography (e.g. Zor et al, 2003;Paul et al, 2006Paul et al, , 2010Hammond et al, 2011;Vanacore et al, 2013;Delph et al, 2015;Tang et al, 2018Tang et al, , 2019Rastgoo et al, 2018;Karabulut et al, 2019). Warren et al (2013) and Delph et al (2015) investigated the crustal structure of the Turkish-Anatolian Plateau using ambient-noise tomography, but their models do not have adequate resolution along the outer limits of the study area because they only used stations located inside Turkey.…”