Crustal and uppermost mantle structure of Caucasus and surrounding regions

A 3-D P-wave velocity model is developed for the crust and uppermost mantle of Caucasus and the surrounding area by applying the tomographic method of Zhao et al. using 300 000 high-quality P-wavefirst arrivals from 43 000 events between 1964 and 2005. This tomographic method can accommodate velocity discontinuities such as the Moho in addition to smooth velocity variations. The spatial resolution is 1°×1° in the horizontal direction and 10 km in depth. The velocity images of the upper crust correspond well with the surface geology. Beneath the southern Caucasus high velocity anomalies are found in the middle crust and low velocity anomalies are found in the uppermost mantle. Relatively low Pn velocities are located under the Lesser Caucasus, eastern Turkey, and northern Iran. Higher Pn velocities occur under the eastern portion of the Black Sea and the southern Caspian Sea, and also extend into the eastern edge of Azerbaijan. Tomographic model significantly reduces the travel-time residuals.