Lateral Variations in Mantle Discontinuity Depth across Antarctica and the Indian Ocean from the Stacking of SS Precursors

• Main Authors: Gao, Stephen S., Liu, Kelly H., Silver, Paul G.
• Format: Text
• Language: unknown
• Published: Scholars' Mine 2000
• Subjects: SEISMOLOGY; Body waves; Core; Lithosphere; Geology; Pacific; Indian; Antarc*; Antarctica
• Online Access: https://scholarsmine.mst.edu/geosci_geo_peteng_facwork/276

We have developed a procedure to stack precursors of SS waves according to their actual raypath and local velocity structures. Data from about 50 western Pacific subduction zone events, recorded by the 80-station broadband South African Seismic Experiment, are used to investigate lateral variations in the depths of mantle discontinuities at SS bounce points. For this geometry, the bounce points are clustered in a nearly NS zone about 7000 km long traversing Antarctica and the Indian Ocean approximately along 100$^o$E longitude. More than 600 strong SS arrivals and their precursors are used in the study. 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 0 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. Significant variations in the apparent depths of the Moho, the 410, and the 670 have been detected. However, there is no clear change corresponding to the midocean ridge. This is consistent with results from other studies using global data sets. Results using the stacking procedure for other areas such as along a 2000 km NW-SE long profile across Braizil will also be presented.