AN ANALYSIS OF THE SKS SPLITTING AT SYOWA STATION IN ANTARCTICA

• Main Authors: クボ アツキ, ヒラマツ ヨシヒロ, カナオ マサキ, アンドウ マサタカ, テラシマ ツトム, Atsuki KUBO, Yoshihiro HIRAMATSU, Masaki KANAO, Masataka ANDO, Tsutomu TERASHIMA
• Format: Report
• Language: English
• Published: Graduate School of Science and Technology, Kobe University:(Present address)National Institute of Polar Research 1995
• Subjects: East Antarctica; Syowa Station; Antarc*; Antarctica
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2782; http://id.nii.ac.jp/1291/00002782/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2782&item_no=1&attribute_id=18&file_no=1

To reveal the seismic anisotropy of the crust and mantle beneath East Antarctica, we have conducted shear wave splitting analysis of SKS waves using STS seismograms at Syowa Station (69.01°S, 39.59°E). The obtained average direction of the fast shear wave was N49°E and the delay time was 0.7s. This delay time was larger than the crustal values in other regions. As the origin of anisotropy in relation to large delay time, we consider three possible mantle flows : 1) present asthenospheric flow due to the plate motion, 2) paleo mantle flow related to Gondwana breakup, and 3) paleo mantle flow that has formed progressive metamorphism and foldings of the Lutzow-Holm Complex in the Late Proterozoic. Neither the direction of present absolute plate motion (N120°E) nor the direction of first breakup of Gondwana at Syowa Station (NW-SE) coincides with the observed direction of anisotropy. From metamorphic studies, the compressional event related to progressive metamorphism has been recognized. The peak metamorphism has been observed along the thermal axis trending NW-SE. Other geologic fabrics around Syowa Station also show that this area has undergone NE-SW compression. We propose that the anisotropy is caused by lattice preferred orientation of mantle minerals along the NE-SW paleo mantle flow.