HR: 17:15h
AN: T52F-06    [PDF]
TI: High-Velocity Lid Structure of East Antarctica and its Implication
AU: * Kuge, K
EM: keiko@kugi.kyoto-u.ac.jp
AF: Dept. Geophysics, Kyoto University, Sakyo, Kyoto, 606-8502 Japan
AU: Fukao, Y
EM: fukao@eri.u-tokyo.ac.jp
AF: ERI, University of Tokyo, Bunkyo, Tokyo, 113-0032 Japan
AB: We determined velocity structure of both P and S waves beneath East Antactica by modeling waveforms of P, PP, S, and SS waves which travel from shallow strike-slip earthquakes in the southwest of New Zealand to broadband stations in Antarctica. In the distance range from 25 to 35 degree, significant phases are observed in the vertical and transverse components of the records, ahead of IASP91 travel times of PP and SS waves, respectively. Our study of travel times and waveforms suggests that the significant phases consist of P (S) wave bottoming at depth shallower than 400 km and PP (SS) waves bouncing at the Moho and Earth surface. The existence of high-velocity lid beneath East Antarctica, which reaches around depth of 200 km, can explain the observed waveforms. By modifying the velocity models of the Canadian shield to fit our observations, we obtained Vp and Vs models of East Antarctica. The velocity of the lid is a few percent slower than that of the Canadian shield. In our observations, S waves bottoming above 400 km are observed at farther distances than P waves. This implies that there can be a difference in the velocity profile between P and S waves. The value of Vp/Vs in our velocity models is around 1.76 for the lid, and larger than 1.8 for the mantle below it. From the velocity models, we examined mantle temperatures, based on the finite strain theory. We used the attenuation model and elastic parameters of Goes et al. (2000). Effect of the anelasticity changes not only Vp and Vs but also Vp/Vs as the functions of temperature and depth. Comparison of Vp/Vs between the calculation and our velocity models shows that the temperatures at the mid depths of the lid and underlying asthenospheric mantle are approximately 500-1000 and 1200-1500 C, respectively. When olivine-rich composition is used, the temperatures tend to be high. Mantle temperatures were also calculated from our Vp and Vs models separately. The temperatures separately obtained from Vp and Vs are in agreement with each other.
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
DE: 8110 Continental tectonics--general (0905)
DE: 9310 Antarctica
SC: Tectonophysics [T]
MN: 2003 Fall Meeting