The structure of the crust in the Turkish–Iranian Plateau and Zagros using Lg Q and velocity

We present a new approach for understanding the origin and nature of seismic anomalies in the continental crust of the Northern Middle East. We have created detailed attenuation (Q_Lg) and velocity (V_Lg) models for the Northern Middle East based on the analysis of waveforms of regional seismic phase Lg from 3171 regional earthquakes recorded at 578 stations in Turkish and Iranian Plateaus and surrounding regions. The attenuation and velocity models are assumed to serve as proxies for the bulk average crustal shear wave attenuation (Q_β) and velocities (V_s). 31 232 reliable Lg spectra were collected and used to measure the two-station method (TSM) and reverse two-station/event method (RTM) Lg Q at 1 Hz (Q₀) and its frequency-dependence factor (η). The Lg Q₀ and η values are measured over the individual TSM and RTM paths and are then used to perform an LSQR tomographic inversion for lateral variations in Q₀ and η. The Lg Q₀ and η models both correlate well with the major tectonic boundaries in the region. The tomographic models as well as the individual TSM and RTM measurements show lower values of Lg Q₀ over the Turkish-Anatolian Plateau (<150) than those observed over the Iranian Plateau (150–400). Furthermore, we obtained the Lg group velocity model by inverting the time of the first arrival of the Lg waveform on each seismogram. Our Q measurements are strongly correlated with the measurements of Lg group velocity (V_Lg) suggesting that the source of many of the low Q and velocity anomalies is likely the same. The regions where we see negative correlations are likely a result of Sn to Lg converted energy. Our results also have implications for the far field ground motions, suggesting that large earthquakes in eastern Iran could have a significant far field ground motions due to relatively low crustal attenuation within the Iranian plateau.