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

Abstract

SUMMARY We have constructed a 3-D shear wave velocity (Vs) model for the crust and uppermost mantle beneath the Middle East using Rayleigh wave records obtained from ambient-noise cross-correlations and regional earthquakes. We combined one decade of data collected from 852 permanent and temporary broad-band stations in the region to calculate group-velocity dispersion curves. A compilation of >54 000 ray paths provides reliable group-velocity measurements for periods between 2 and 150 s. Path-averaged group velocities calculated at different periods were inverted for 2-D group-velocity maps. To overcome the problem of heterogeneous ray coverage, we used an adaptive grid parametrization for the group-velocity tomographic inversion. We then sample the period-dependent group-velocity field at each cell of a predefined grid to generate 1-D group-velocity dispersion curves, which are subsequently inverted for 1-D Vs models beneath each cell and combined to approximate the 3-D Vs structure of the area. The Vs model shows low velocities at shallow depths (5–10 km) beneath the Mesopotamian foredeep, South Caspian Basin, eastern Mediterranean and the Black Sea, in coincidence with deep sedimentary basins. Shallow high-velocity anomalies are observed in regions such as the Arabian Shield, Anatolian Plateau and Central Iran, which are dominated by widespread magmatic exposures. In the 10–20 km depth range, we find evidence for a band of high velocities (>4.0 km s–1) along the southern Red Sea and Arabian Shield, indicating the presence of upper mantle rocks. Our 3-D velocity model exhibits high velocities in the depth range of 30–50 km beneath western Arabia, eastern Mediterranean, Central Iranian Block, South Caspian Basin and the Black Sea, possibly indicating a relatively thin crust. In contrast, the Zagros mountain range, the Sanandaj-Sirjan metamorphic zone in western central Iran, the easternmost Anatolian plateau and Lesser Caucasus are characterized by low velocities at these depths. Some of these anomalies may be related to thick crustal roots that support the high topography of these regions. In the upper mantle depth range, high-velocity anomalies are obtained beneath the Arabian Platform, southern Zagros, Persian Gulf and the eastern Mediterranean, in contrast to low velocities beneath the Red Sea, Arabian Shield, Afar depression, eastern Turkey and Lut Block in eastern Iran. Our Vs model may be used as a new reference crustal model for the Middle East in a broad range of future studies.

Asthenospheric Flow of Plume Material Beneath Arabia Inferred From S Wave Traveltime Tomography

“…Instead, a priori 3‐D crustal model can be used to calculate the traveltime differences between the 3‐D crustal model and 1‐D reference model and then correct traveltime residuals to remove the crustal effect. Although there are high‐resolution regional crustal models for parts of our study region (e.g., Hammond et al, 2011; Kaviani et al, 2020; Tang et al, 2019), there are few regional models that cover the entire area from northeast Africa to Arabia. Therefore, for consistency we use the CRUST1.0 model (Laske et al, 2013), a global crustal model made from a compilation of various sources of information on a 1° × 1° grid, for the crustal correction.…”

Crustal Structure of the Mesopotamian Plain, East of Iraq

“…Figures 3 and 4 show these stacked and individual moveout corrected receiver functions. Dispersion data for Rayleigh wave group velocity come from the ambient noise tomography of Kaviani et al (2020). The group velocities were measured for the region in the period range of 5–100 s. The group velocity maps were interpolated to obtain a site‐specific dispersion curve.…”

“…Receiver Function data used in this study are made available online (at https://data.mendeley.com/datasets/8m9ydb3wds/1). Dispersion data are available through Kaviani et al (2020). Continuous data from five of the used stations are broadcasted on real time to the Incorporated Research Institutions for Seismology (IRIS), and they are unrestricted for use by all interested researchers.…”

“…The teleseismic data were used to obtain 1‐D S velocity structure beneath each station using joint inversion of P receiver function and Rayleigh wave dispersion (Julia et al, 2000). For each station, one high‐quality stacked receiver function was calculated and jointly inverted with fundamental mode Rayleigh wave group velocity extracted from an ambient noise tomography for the Middle East (Kaviani et al, 2020). The resulting models reveal unexpected crustal thickness variations beneath the Mesopotamian Plain.…”

The structure of the lithosphere and upper mantle beneath the Eastern Mediterranean and Middle East

“…Therefore the structure appears to be a piece of thick cratonic lithosphere that has been pulled down 4 km below sea level, either by local convective downwelling as Woodside (1976) suggested, or by the negative convective buoyancy transmitted through the lithosphere from the slab beneath the Aegean. Further east Skobeltsyn et al (2014) and Kaviani et al (2020) have used the dispersion of fundamental-mode Rayleigh waves, either from earthquakes or from noise, to produce three dimensional models of the V s structure beneath much of the Middle East. They found low velocities in regions where the lithosphere in Fig.…”