Lateral variations in mantle P velocity for a tectonically regionalized earth
Estimates of tau functions for a tectonically regionalized earth are obtained from over 1.25 million seismic ray paths of ISC Bulletin data to study the correlation of lateral variations in mantle P velocity with surface heterogeneity. Statistical regularity criteria check the consistency of the regionalization. Tau perturbations attributed to crustal and shallow-mantle velocity variations are also estimated. ''Single region'' tau functions are constructed and inverted to obtain velocity-depth functions and extremal bounds at the 99.9% confidence level for seven different types of tectonic regions. Deviations from a regionally weighted reference mean velocity function indicate significant differences, particularly between oceanic and continental tectonic regions, extending to a depth of 700 km. Increased shallow-mantle velocities are observed from young to old oceans and from active to stable continents. Evidence for a velocity anomaly between 700 and 950 km is indicated. Significant negative residuals are observed centered at about 780 km depth below young oceans and about 880 km below active continents. The level of variations decreases below 950 km. Lateral velocity variations are also suggested within 250 km of the core boundary. Tau perturbations are indicative of negative shallow-mantle velocity anomalies beneath oceanic regions and positive anomalies beneath continental regions and oceanic trenches. A less than average crustal thickness in oceans and greater thickness in stable continents are also indicated.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA). Center for Computational Seismology; California Univ., Berkeley (USA). Dept. of Geology and Geophysics
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5414226
- Report Number(s):
- LBL-21596; ON: DE86015136
- Resource Relation:
- Other Information: Thesis. Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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