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 broadband stations in the region to calculate group-velocity dispersion curves. A compilation of > 54000 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) 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.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): BAS/1/1339-01-01
Acknowledgements: The authors would like to thank three anonymous reviewers for providing valuable comments and suggestions that improved the initial and revised versions of the manuscript. This study was possible thanks to the availability of continuous daily record of seismic noise from permanent and temporary stations operating in the region. Data was provided by different seismological networks and data centers. The Iranian Seismological Center (Institute of Geophysics, University of Tehran) and International Institute of Earthquake Engineering and
Seismology (IIEES) gratefully provided the daily noise record from the permanent broadband stations in Iran. Continuous records from Kandilli Observatory Digital Broadband Seismic Network (doi: 10.7914/SN/KO, Kandilli Observatory and Earthquake Research Institute,
Bosphorus Univ. (2001)) and Israeli Broadband Seismological Network (GII-Net, network code IS) were downloaded from the European Integrated Data Archive (EIDA). The facilities of IRIS Data Services and specifically the IRIS Data Management Center were used to access data of temporary stations and global permanent stations used in this study. IRIS Data Services are funded through the Seismological Facilities for the Advancement of Geoscience and EarthScope (SAGE) Proposal of the National Science Foundation under cooperative agreement EAR1261681. The seismological networks providing data to us via the IRIS data service are listed in the Supplementary Information. Rayleigh wave group-velocity dispersion data from the Saudi National Seismic Network (SNSN) operated by the Saudi Geological Survey was taken from previous studies (Tang et al., 2018, 2019) of the seismology group (PMM and ZT) from the King Abdullah University of Science and Technology (KAUST). PMM and ZT were supported by grant BAS/1/1339-01-01 funded by the
KAUST. We adopted the algorithm introduced by Boué et al. (2014) and used the WHISPER software package (Briand et al., 2013) to preprocess individual daily vertical-component records. Seismic analysis was conducted using the routines implemented in the Python package ObsPy (Beyreuther et al, 2010). The maps shown in the paper were created using the Generic Mapping Tools (Wessel et al.,
2013). S.P. acknowledges support from Natural Environmental Research Council (NERC) grant NE/R013500/1 and from the European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement 790203. S.P. is grateful to the NCM for providing continuous passive seismic data used in this study.