Accession Number : ADA310351

Title :   Uppermost Mantle Structure in Southern Eurasia from PN Tomography and Sn Attenuation.

Descriptive Note : Final technical rept. 1 Jul 93-31 Dec 95,

Corporate Author : NEW MEXICO STATE UNIV LAS CRUCES DEPT OF PHYSICS

Personal Author(s) : Hearn, Thomas M. ; Ni, James F.

PDF Url : ADA310351

Report Date : JUN 1996

Pagination or Media Count : 60

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.

Descriptors :   *TOMOGRAPHY, *SEISMOLOGY, PROPAGATION, MIDDLE EAST, BOUNDARIES, MOUNTAINS, LIMITATIONS, ATTENUATION, MAPPING, EARTH MODELS, EURASIA, EARTH MANTLE, TECTONICS.

Subject Categories : Geology, Geochemistry and Mineralogy

Distribution Statement : APPROVED FOR PUBLIC RELEASE