High Resolution 3D Wavespeed Model of the Iranian Plateau Lithosphere

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

The Iranian Plateau forms a broad zone of deformation located between the Arabian and Eurasian Plates. The Arabian-Eurasian collision is similar to the Indo-Eurasian which formed the Himalaya and Tibet but is much younger. Studies of the Iranian Plateau can provide clues to understanding the earlier stages of the continent-continent collision process. To determine the lithospheric structure of this region we determine fundamental mode Rayleigh wave group velocity for 5-70 s periods using large regional earthquake and ambient noise data sets. We build Rayleigh wave tomographic maps including both isotropic and azimuthal anisotropic terms for group velocity. At short periods (<20s) there is no clear anisortopic pattern; at longer periods (>20s) the azimuthal anisotropy trends are more uniform. The southern Zagros, central and eastern Iran and Kopeh-dagh show NE-SW anisotropic trends which are close to reported GPS velocity vectors; the northern part of Zagros shows NW-SE trend and an E-W orientation is dominant in the Alborz and northwest Iran. To achieve a more detailed 3D Vsv models we jointly inverted the group velocity dispersion with P-wave receiver functions at more than 200 seismograph sites in the Zagros Mountains and Iranian Plateau obtaining a high resolution wavespeed model for the crust and uppermost mantle. The crust is as great as 60 km thick below the Zagros Mountains and 50 km thick beneath the Alborz Mountains but thinner (35-45 km) below the central Iranian Plateau. The low shear velocity anomalies of the upper crust correspond to the regions of thick sediments such as Caspian Basin, Zagros fold and thrust belt, Makran accretionary zone, and central Iran basin. The Sanandaj-Sirjan metamorphic zone and the Lut block show higher velocities for the upper crust. In the lower crust there is a boundary separating low-velocity Zagros from the rest of Iran, the deeper parts, representing the uppermost mantle, show higher velocities for Zagros which we interpreted as a thick lithospheric Zagros root compared to a thin lithosphere beneath central Iran

Presenting Author: Mohsen Irandoust

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