Different anisotropic patterns from shear-wave splitting in Ryukyu arc and southeast China
Speaker: Hsiao-Chuan Peng Adviser: Hao Kuo-Chen
Abstract
Shear-wave splitting is an important measurement to understand the vertical anisotropic variation beneath seismic stations. Depends on different wave frequency, the splitting parameters (ϕ, δt) will show different patterns from different anisotropic depths. For Ryukyu trench, the splitting times ranged from 0.25 to 2 s, most values were between 0.75 and 1.25 s, and the fast directions were parallel to the strike of the trench and perpendicular to the convergence direction. These anisotropic patterns may relate to the observation of corner flow in the mantle wedge combined with b-type olivine fabric. In this model, the flow direction in the wedge is perpendicular to the trench, but the fast axes of olivine crystals tend to align perpendicular to the flow direction, resulting in trench-parallel shear wave splitting. For Fujian Province, the average normalized slow wave time delay is 2.5 ± 1.5 ms/km and the highest values extend over coastline. There are two predominant polarization directions, in NE and NW directions, in accordance with the two series of crossing faults, also means that the regional stress field is mainly influenced by the two groups of faults. As a result, the magnitude of anisotropy beneath Fujian Province seems to be consistent with the most seismically active area.
Reference
M.D. Long, R.D. van der Hilst, Shear wave splitting from local events beneath the Ryukyu arc: Trench-parallel anisotropy in the mantle wedge, Phys. Earth Planet. Inter., 155 (2006), pp. 300–312
<full text>
Y. Gao, J. Wu, J.A. Cai, Y.T. Shi, S. Lin, T. Bao, Z.N. Li, Shear-wave splitting in the southeast of Cathaysia block, South China, Journal of Seismology, 13 (2) (2009), pp. 265–275
<full text>
J. Park and V. Levin, Seismic anisotropy: tracing plate dynamics in the mantle, Science, 296 (5567) (2002), pp. 485–489