HR: 0800h
AN: T21C-0517    [Abstracts]
TI: fine structure of 410km discontinuity beneath the Southern Europe
AU: * Wan, K
EM: wks@ustc.edu
AF: school of earth & space sciences, Univ. Sci. Tech of China, 96 Jinzhai Road, Hefei, ANH 230026 China
AU: Wan, X
EM: wanxin1030@ustc.edu
AF: school of earth & space sciences, Univ. Sci. Tech of China, 96 Jinzhai Road, Hefei, ANH 230026 China
AU: ni, s
EM: sdni@ustc.edu.cn
AF: school of earth & space sciences, Univ. Sci. Tech of China, 96 Jinzhai Road, Hefei, ANH 230026 China
AB: In the distance range of 10-14 degrees, P waves from the topside reflection off the 410km discontinuity are very sensitive to the fine structure of the discontinuity. We analyzed 49 broadband seismograms from an earthquake ( May 18, 1998) in Italy (Mw 5.8) , recorded by Orfeus and SZGRF networks. Distances between the source and the stations were from 9° to 19°, and provided a detailed look at the 410km structure. On the other hand, the azimuth of these records were in a narrow range from 334° and 356°, so the differences in azimuth may have little effects on the waveforms. From our observation, P410 phase has little change in amplitude when the distance decreases from 15° to about 11.5°. However, an abrupt termination was observed from distance 11° to 10.5°. These features cannot be explained with PREM model. We calculated several groups of models with F-K method and compared their synthetic seismograms with the observed one. These models are: 1) two-step sharp jump models, with different thickness; 2) linear models; 3) linear-sharp jump models[Tim Melbourne, Don Helmberger, Journal of Geophysical Research, 1998]; 4) models calculated from a mineralogical model[Gaherty, Wang, Geophysical research letters, 1999]; Features in the observed waveform can be well modeled with model 3 and 4 while only parts of them fitted to model 1 or 2. But when we calculated with a less detailed model, seismograms of model 4 should have more noise than model 3. In conclusion, the structure of 410km discontinuity can be considered as a linear-sharp velocity jump, which is consistent with mineralogical models.
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Tectonophysics [T]
MN: Fall Meeting 2005