Accession Number : ADA291074

Title :   Mapping Crust and Upper Mantle Structure Beneath Southern Eurasia.

Descriptive Note : Final technical rept. 1 Sep 92-31 Aug 94,

Corporate Author : CALIFORNIA INST OF TECH PASADENA SEISMOLOGICAL LAB

Personal Author(s) : Helmberger, Donald V.

PDF Url : ADA291074

Report Date : 09 JAN 1995

Pagination or Media Count : 70

Abstract : Travel-time tomography was used to obtain the lateral variations in P(n) velocities and P(n) velocity azimuthal anisotropy beneath the Basin and Range Province. We used 1226 P(n) arrivals from 184 earthquakes recorded by 113 stations. The tomographic image shows the lateral variation in P(n) velocity from 7.9 km/s in the northern Province to 7.6 km/s in the southern Province. Azimuthal variations in P(n) velocities are less than one percent as determined from the travel time residuals after taking out the contribution of the lateral velocity variations of the P(n) tomography. Although the standard errors of the azimuthal variations are about two percent, there is no reason to believe the existence of the P(n) azimuthal anisotropy in the uppermost mantle beneath the Basin and Range Province. Beghoul and Barazangi's (1990) suggestion of more than three percent azimuthal anisotropy is the result of the lateral heterogeneity and mantle velocity gradient Before tomographic inversion, we refined the P(n) travel times by considering the lateral variations in the crustal thickness and velocities in the region based on the numerical experiment and theoretical development given in this paper. These refinements are crucial in obtaining an accurate velocity image. (MM)

Descriptors :   *EARTH CRUST, *EARTHQUAKES, *PLATE TECTONICS, *EARTH MANTLE, FAULTS(GEOLOGY), TOMOGRAPHY, SEISMIC VELOCITY, BASINS(GEOGRAPHIC), SEISMOLOGY, EURASIA, PRIMARY WAVES(SEISMIC WAVES), SECONDARY WAVES.

Subject Categories : Geology, Geochemistry and Mineralogy
      Seismology

Distribution Statement : APPROVED FOR PUBLIC RELEASE