Lateral Variation of Mantle Discontinuities from the Stacking of SS Precursors
Data from several subduction zone events from the west coast of South America and recorded by the on-going broadband South African Seismic Experiment, are used to investigate lateral variations in mantle discontinuities at SS bounce points. For this geometry, the bounce points are clustered in a NNE-SSW zone of about 2000 km long traversing part of the Atlantic basin and the the NE part of the South American continent. We exploit the close bounce-point spacing to stack traces of nearby stations according to the predicted differential time between SS precursors and SS. We consider candidate discontinuity depths in the range 5 to 800 km in increments of 2.5 km. Traces within overlapping spatial windows of 400 km by 400km are stacked to obtain a spatially smoothed discontinuity profile. Preliminary results show clear SS precursors and significant lateral variation in transition zone discontinuities. The depth of the 410km discontinuity ranges from 400 to 405 km. The 660 km discontinuity shows greater variation. Beneath the northern half of the profile it ranges from 655 to 663 km; and beneath the southern half of the profile it decreases from 660 km to 645 km toward the south, over a distance of 900 km. The resulting estimates of transition zone thickness are about 260 km in the north and 240 km in the south, which, if thermally induced, suggests a temperature variation of about 140⁰C, with higher temperatures to the south. Stacking at various of frequency bands reveals the 660km discontinuity is thicker than the one at 410km.
S. S. Gao and P. G. Silver, "Lateral Variation of Mantle Discontinuities from the Stacking of SS Precursors,", vol. 79 American Geophysical Union (AGU), Dec 1998.
AGU Fall Meeting (1998: Dec. 1, San Francisco, CA)
Geosciences and Geological and Petroleum Engineering
Article - Conference proceedings
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