HR: 17:00h
AN: S14A-05 INVITED    [Abstracts]
TI: PKPPcP or P'P' precursor from a 785km discontinuity?
AU: * ni, s
EM: sdni@ustc.edu.cn
AF: National Geophysical Observatory at MengchehengSchool of Earth and Space Sciences, Univ. Sci. & Tech. of China, 96 Jinzhai Road, hefei, anh 230026, China
AU: Zeng, x
EM: zengxf@mail.ustc.edu.cn
AF: National Geophysical Observatory at MengchehengSchool of Earth and Space Sciences, Univ. Sci. & Tech. of China, 96 Jinzhai Road, hefei, anh 230026, China
AU: Cormier, V
EM: vernon.cormier@uconn.edu
AF: University of Connecticut, 2152 Hillside Road, U-3046, Storrs, CT 06269-3046, United States
AB: Precursors of P'P' around 80 degrees are very useful for studying discontinuities in the Earth, particularly the 410km and 660 km discontinuities. P'P' precursors from deeper discontinuities, however, can be contaminated by the PKPPcP (or PcPPKP) phase, which is strongest around the antipode and extends to 275 degrees according to geometric ray theory. Because P velocity in the outer core is much lower than that in the lower mantle, tunneling effects are prominent for distances larger than 250 degrees, and PKPPcP becomes PKPPdiff for distances larger than 275 degrees. We first apply normal mode summation to study the amplitude of PKPPcP vs distance, which predicts PKPPcP to be a strong phase for distances well beyond 280 degress at 0.1HZ. Then we apply full wave technique to modeling of PKPPcP's amplitude at distances from 210 to 310 degrees for 0.1 HZ---2 HZ, and find that PKPPcP is strong phase for distances around 280 degrees and 0.3 Hz, but is very weak at 1Hz. The frequency dependence of PKPPcP amplitude agrees well with the P'P' precursor observations of le Stunff et al. (1995), which were best observed in a low frequency band (0.01 to 0.3 Hz), disappearing at higher frequency (around 1HZ). Thus the P'P' precursor are better interpreted as PKPPcP, instead of reflection by a 785km discontinuity beneath Africa. The relatively strong amplitude of PKPPcP beyond 280 degrees makes P'P' precursors less applicable for discontinuities deeper than 660km.
DE: 7203 Body waves
DE: 7290 Computational seismology
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Seismology [S]
MN: 2007 Fall Meeting