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Abstract: This project has investigated the seismic characteristics of southern Eurasia through Pn travel time tomography and the regional mapping of attenuation for high frequency Sn and Lg waves. Pn tomography results indicate that much of the uppermost mantle beneath southern Eurasia has low P-wave velocity and a small amount of melt. Mapping of Sn propagation efficiency confirms that regions with low Pn velocity generally do not propagate Sn waves efficiently. This is especially true for the Turkish-Iranian Plateau and the northern Tibetan Plateau. In contrast to Sn waves, Lg waves propagate within the crust and are insensitive to mantle properties, but are affected by changes in crustal structure. Lg is weakened or completely absent when propagation paths obliquely cross major tectonic boundaries such as the Himalaya Mountains, the Tarim Basin, the Caucasus Mountains, or the oceanic crust of the Black and Caspian Seas. The high attenuation of Sn in many parts of southern Eurasia limits its use in regional nuclear monitoring; however, Lg can be observed provided data is available from stations sited within each geologic province.
Regional studies serve a twofold purpose: (1) regional data can provide stable yield estimates for underground nuclear explosions, and (2) regional data can discriminate between explosions and earthquakes. For both these goals, understanding the timing and strength of regional seismic phases is critical.