Mantle Layering beneath GSN Stations from Nonlinear Stacking of P-to-S Converted Waves
Seismic velocity discontinuities in the mantle represent sudden changes in chemical composition and/or mineralogical phases. The existence of such changes and the depths at which they take place are important for understanding the dynamic and chemical processes in the mantle. By taking the advantage of the dramatic progress in computing speed and storage capabilities, we have collected up to about a thousand high quality broadband seismograms for each of the approximately 100 Global Seismic Network stations, and stacked the source-normalized traces according to the computed theoretical arrivals of P-to-S converted phases for the depth range of 0 to 1000 km. For each station, we have also stacked traces coming from successive azimuthal bands for both the radial and transverse components. Some preliminary observations include: (1). The first order mantle discontinuities including the Moho, the 410, and the 670 are clearly observed beneath all the stations if the number of high quality events are 80 or more; (2). The well-known transition zone discontinuity at about 520 km depth is not a global feature that is capable of generating P-to-S converted phases; (3). More than half of the stations with sufficient number of high quality events show two clear discontinuities in the upper mantle, one is at 250 km, and the other is at 330 km; (4). Beneath stations where subducting slabs are expected to reach the 670 km discontinuity, the 670 is more diffusive than that beneath other stations; (5). Clear azimuthal variations of the depths of the discontinuities and the amplitudes can be observed on some of the stations.
K. H. Liu et al., "Mantle Layering beneath GSN Stations from Nonlinear Stacking of P-to-S Converted Waves,", vol. 82, no. 47 American Geophysical Union (AGU), Dec 2001.
AGU Fall Meeting (2001: Dec. 10-14, San Francisco, CA)
Geosciences and Geological and Petroleum Engineering
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© 2001 American Geophysical Union (AGU), All rights reserved.
01 Dec 2001