11:15 AM - 11:30 AM
[S14-2-04] Upper-Mantle Discontinuities Across Stable South American Continent
We stacked receiver function traces from all permanent stations of the Brazilian Seismographic Network (RSBR), as well as stations from a temporary experiment (3-Basins Project) along the SW Brazilian border, to obtain cross-section images of the major upper-mantle discontinuities in the stable South American continent.
We selected events with magnitudes > M5 in the distance range 30 to 95 degrees, visually inspected all traces, confirmed the incoming P-wave azimuth, rotated into the LQT system (using the estimated azimuth and theoretical incidence angle), deconvolved to obtain the Q-component receiver functions, and stacked along profiles. Deconvolution used a high-pass filter at 0.02Hz. Before stacking, all traces were move-out corrected to a ray-parameter of 6.4 s/deg allowing for stacking traces from different events in different stations with the same piercing-point. Stacking was done by considering piercing point locations at a depth of 520 km. Interpretation and results will be presented along sections constructed to image the major tectonic provinces in South America.
Most of the study region showed both 410- and 660-km discontinuities at the expected depths. Variations observed are mostly related to the craton high-speed roots that shift up time images of the discontinuities beneath cratonic areas. This effect can be seen beneath the San Francisco craton and the Amazon craton. A newly observed feature is the influence of the cold Nazca Slab in lowering the 660-km discontinuity under the Pantanal/Chaco basin. The flat geometry of the Nazca slab beneath the Pantanal Basin makes it closer to the 660-km discontinuity, which could potentially help to interpret the formation and evolution of the Pantanal Quaternary Basin.
We selected events with magnitudes > M5 in the distance range 30 to 95 degrees, visually inspected all traces, confirmed the incoming P-wave azimuth, rotated into the LQT system (using the estimated azimuth and theoretical incidence angle), deconvolved to obtain the Q-component receiver functions, and stacked along profiles. Deconvolution used a high-pass filter at 0.02Hz. Before stacking, all traces were move-out corrected to a ray-parameter of 6.4 s/deg allowing for stacking traces from different events in different stations with the same piercing-point. Stacking was done by considering piercing point locations at a depth of 520 km. Interpretation and results will be presented along sections constructed to image the major tectonic provinces in South America.
Most of the study region showed both 410- and 660-km discontinuities at the expected depths. Variations observed are mostly related to the craton high-speed roots that shift up time images of the discontinuities beneath cratonic areas. This effect can be seen beneath the San Francisco craton and the Amazon craton. A newly observed feature is the influence of the cold Nazca Slab in lowering the 660-km discontinuity under the Pantanal/Chaco basin. The flat geometry of the Nazca slab beneath the Pantanal Basin makes it closer to the 660-km discontinuity, which could potentially help to interpret the formation and evolution of the Pantanal Quaternary Basin.