Mapping Crust and Upper Mantle Structure Beneath Southern Eurasia.
Final technical rept. 1 Sep 92-31 Aug 94,
CALIFORNIA INST OF TECH PASADENA SEISMOLOGICAL LAB
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Travel-time tomography was used to obtain the lateral variations in Pn velocities and Pn velocity azimuthal anisotropy beneath the Basin and Range Province. We used 1226 Pn arrivals from 184 earthquakes recorded by 113 stations. The tomographic image shows the lateral variation in Pn velocity from 7.9 kms in the northern Province to 7.6 kms in the southern Province. Azimuthal variations in Pn 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 Pn tomography. Although the standard errors of the azimuthal variations are about two percent, there is no reason to believe the existence of the Pn azimuthal anisotropy in the uppermost mantle beneath the Basin and Range Province. Beghoul and Barazangis 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 Pn 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
- Geology, Geochemistry and Mineralogy