HR: 0830h
AN: S21F-0383    [PDF]
TI: Crustal_@Structure Derived From Refractions and Wide-Angle Reflections in The Mizuho Plateau, East Antarctica
AU: * Yoshii, K
EM: yoshii@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Ito, K
EM: ito@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Kanao, M
EM: kanao@nipr.ac.jp
AF: National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo, 173-8515 Japan
AB: In 1999-2000, the 41st Japanese Antarctic Research Expedition (JARE41) conducted high density seismic experiments from the coast and inland on the Mizuho Plateau, East Antarctica, along a 180km line with station spacings of 1km. In the record sections, we can pick direct waves through the ice sheets along with refracted and reflected waves from the crust and the Moho boundaries. Previously in 1980-1981, JARE21 and JARE22 conducted large seismic explosion experiments that extended along a 300km line in the same area, although the station spacing is larger, about 10km. Some of the recorded data show especially clear waves refracted and reflected from the crust and the Moho boundaries, and the coverage of first arrivals extends from about 50 to 300km. These travel time data provide good information for investigating the deep structure in the crust. Therefore, we tried to determine a more detailed P-wave velocity model from analysis of the combined data of these two experiments using the ray tracing technique of Zelt (1992, 1994). From the results of the analyses, we conclude that the ice sheet has a 60-100m thin surface layer with a P-wave velocity of 2.6-3.0km/s underlain by an ice sheet layer with a P-wave velocity of 3.8km/s. This velocity change in the ice sheet is consistent with that of the ice density obtained from the core drilled at the end of the observation line. The uppermost layer of the crust has a P-wave velocity of 6.2km/s, and is likely to be the old mafic rocks of the Precambrian shield located just below the ice sheet, which are seen at nearby outcrops. An abrupt valley-shaped change of the first layer is found in the middle of the observation line of JARE41. This is consistent with the variation in gravity anomalies and shows the change in the topography of the basement rock. Furthermore, a P-wave velocity of about 6.1km/s at the bottom of this valley structure, fit the observed travel times better than a velocity of 6.2 km/s, suggesting that there are moraines or weathered rocks in the valley. The crust consists of two additional layers; the second layer has a P-wave velocity of about 6.4-6.5km/s and the third layer has a velocity of about 6.6-6.9km/s. Clear reflections are observed from the upper boundary of the 6.4km/s layer. There are other reflected waves that do not seem to correspond to the above mentioned boundaries. The Moho reflections are also well observed and the Moho depth is about 40km with a gentle dip towards the inland direction.
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2003 Fall Meeting