Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.s41b..01k&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #S41B-01
Other
7203 Body Wave Propagation, 7207 Core And Mantle
Scientific paper
Indications of lower mantle discontinuities are known for decades, but still little is known about their properties, and their origins are enigmatic. For example, in our recent studies, broadband seismograms of deep events have been explored with the aid of a novel technique (Vinnik et al., 1998, 2001). In our data there are indications of discontinuities near 860-880 km, 1010-1120 km, 1170-1250 km, 1340-1430 and 1670 - 1800 km depths, and the clearest signals are obtained from the discontinuity at a depth of 1200 km in several subduction zones. On the other hand, from the analyses of short-period array data, the presence of ``mid-mantle discontinuities" at depths of 900-1100km has been shown (Kawakatsu and Niu, 1994; Niu and Kawakatsu, 1997). The presence of dipping discontinuities/scatterers in the lower mantle has been also confirmed from short-period array data (Kaneshima and Helffrich, 1998, 1999; Castle and Creager, 1999). The emerging results from the broadband and short-period array analyses do not necessarily give a consistent picture, and the situation seems rather confusing. In hope for clarifying the situation, results of a consistent analysis of data from the high density (& quality) broadband and short-period arrays recently deployed in the Japanese islands will be shown. We especially focus on the mid- and lower-mantle structure beneath the Tonga and Indonesia arcs. The questions to be addressed also include (1) should subducted oceanic crusts in the lower mantle all explain these discontinuities/scatterers, (2) is there any evidence for the postulated deep chemical boundary (Kellogg et al., 1999)? \small Castle, J. C and K. C. Creager (1999), J. Geophy. Res., 104, 7279-7292. Kaneshima, S. and G. Helffrich (1998), J. Geophy. Res., 103, 4825-4838. Kaneshima, S and G. Helffrich (1999), Science, 283, 1888-1891. Kawakatsu, H., and F. Niu (1994), Nature, 371, 301-305. Kellogg, L. H., et al. (1999), Science, 283, 1881-1884. Niu, F., and H. Kawakatsu (1997), Geophys. Res. Lett., 24, 429-432. Vinnik, L et al. (1998), Earth, Planets, Space, 50, 987-997. Vinnik, L., et al. (2001), Geophys. J. Inter, in press.
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