Crustal and upper mantle model of the Middle East based on full-waveform inversion

Summary

We present MEAD-M20 (Middle East ADjoint-Model20), a new tomographic model of the Middle East and its surrounding regions, including Anatolia, Iran, and the Caucasus. The model is developed within a full-waveform inversion framework, based on 3D numerical wavefield simulations and the adjoint method, after 20 conjugate gradient iterations, utilizing an extensive dataset from permanent and temporary stations available from EarthScope and regional networks, such as Kandilli Observatory, the Mesopotamian Seismological Network of Iraq, the International Institute of Earthquake Engineering and Seismology of Iran and additional data made available from the Saudi Geological Survey. Starting from the global full-waveform inversion model GLAD-M25 (Lei et al. 2020) on a 60○ × 60○ regional mesh, we invert 210 regional earthquakes recorded by 1,215 stations to obtain the P- and S-wave model with shear-wave transverse isotropy confined to the upper mantle. During the first 12 iterations, we use two period bands, combining multitaper traveltime measurements of 15–50 s body waves and 50–100 s body and surface waves on three components. We use a refined crustal mesh to better sample the crust after the 12th iteration and gradually decrease the minimum surface-wave period to 30 s. MEAD-M20 provides a self-consistent P- and S-wave model ready for seismic wave simulations, which is essential for accurate earthquake location, source parameter estimation, and seismic hazard assessment in regions such as the Middle East, where complex geology and tectonics prevail. MEAD-M20 reveals several important geodynamical and tectonic features, including local mantle plumes beneath the Arabian Plate, Jordan, and the Levant, characterized by low-velocity anomalies and likely associated with volcanism in the Harrats, Jordan, and Karacadağ regions. In addition to the active subduction and rifting in the area, the model clearly identifies remnants of the Tethys Ocean beneath Eastern Anatolia, which become progressively shallower toward the Makran region in the south, consistent with the subduction history along the Bitlis–Zagros suture zone. We also observe lithospheric-scale low-velocity anomalies associated with the North and East Anatolian faults, extending to depths of approximately 200 km.