Accession Number : ADA295089

Title :   Fine Scale Structure of the Eurasian Crust and Upper Mantle from High-Frequency Waves.

Descriptive Note : Final technical rept.,

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF EARTH ATMOSPHERIC AND PLANETARY SCIENCES

Personal Author(s) : Jordan, Thomas H.

PDF Url : ADA295089

Report Date : 10 APR 1995

Pagination or Media Count : 72

Abstract : The purpose of this project is to provide a better understanding the effects of small-scale inhomogeneities on high-frequency waves excited by nuclear explosions, especially at regional distances. In this project, the PI and students developed and applied methods for extracting phase Uclays and amplitudes from three-component seismograms. These methods delivered new information about impedance discontinuities and velocity gradients in the upper mantle, and large data sets were inverted for radially anisotropic structure. The principle result of this analysis was that the magnitude of the anisotropy observed beneath western Australia and the western Pacific required stochastic variations of isotropic velocities that were petrologically unreasonable, and local anisotropy was inferred. The depth extent of anisotropy is limited to 250 km beneath Australia and 170 km beneath the Pacific. No azimuthal anisotropy was observed in either region, establishing the characteristic outer scale length of the heterogeneous anisotropic structure to be less than 3000 km. This report is split into two sections: the first presents the results for the Australian upper mantle, and has been accepted for publication in Science; the second presents the Pacific results, and has been submitted to Journal of Geophysical Research. (MM)

Descriptors :   *NUCLEAR EXPLOSIONS, *EARTH CRUST, *SEISMIC WAVES, *EARTH MANTLE, HIGH FREQUENCY, EXPLOSION EFFECTS, WAVE PROPAGATION, GEOPHYSICS, REFLECTIVITY, DISCONTINUITIES, SEISMIC VELOCITY, EURASIA, TRAVEL TIME, PRIMARY WAVES(SEISMIC WAVES), SCIENTIFIC LITERATURE, SECONDARY WAVES, SEISMOGRAPHS.

Subject Categories : Seismology
      Nuclear Weapons

Distribution Statement : APPROVED FOR PUBLIC RELEASE