HR: 08:45h
AN: V41A-02 INVITED     [Abstracts]
TI: Lower Mantle Tomography and D" Triplications
AU: * Helmberger, D
EM: helm@gps.caltech.edu
AF: Caltech Seismo Lab., l200 E. California Blvd, Pasadena, CA 91125 United States
AU: Sun, D
EM: sdy@gps.caltech.edu
AF: Caltech Seismo Lab., l200 E. California Blvd, Pasadena, CA 91125 United States
AU: Ni, S
EM: stone@gps.caltech.edu
AF: Caltech Seismo Lab., l200 E. California Blvd, Pasadena, CA 91125 United States
AB: A relatively strong secondary phase (Scd) occurs between S and ScS beneath regions with relatively fast velocities in tomographic images; Alaska, Northern Eurasia, India, Central America, etc. The latter images are usually interpreted as cool slab material subducted around the circum-Pacific. Sidorin et al. (1999) argued that the triplication (Scd) is controlled by the combination of these enhanced velocity gradients (Grand's model) and a small positive velocity jump (1.5%) induced by a phase-change, occurring at a reference depth of 200 km with a clapreyron slope of about 6MPa/k (possible Post-Perovskite). Assuming such a mechanism, we can predict the elevation of the discontinuity above the CMB globally using thermal anomalies inferred from tomographic models. Many of the observed variations in travel time and amplitude Scd (triplicated phase) can be predicted by this model where the differential times reach a few seconds and the amplitude (Scd/S) ratios reach 50%. Strengths in the Pacific fall below 10% where only stacking can resolve such small features making it difficult to map coherent boundaries. After reviewing the 2D analyses producing these features, we present some new waveform modeling results introduced by more complex velocity-temperature mapping and explore 3D effects beneath Central America, where vary rapid changes in Scd are observed.
DE: 8400 VOLCANOLOGY
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2005 Joint Assembly