Study on shear wave structure for the crust in the Lützow-Holm Bay region, East Antarctica
金尾, 政紀
Crustal structure in the Lutzow-Holm Bay region (LHB) , East Antarctica, was investigated by using seismological waveform data obtained from refraction experiments and local telemetry networks, together with broadband seismographs at Syowa Station (SYO; 69.0°S, 39 .6°E). Crustal models for explaining shear waves' propagation in this region were calculated, in particular concerning crustal heterogeneity. At first, local earthquakes detected by telemetry networks in 1987-1989 were analyzed by
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... ting the lapse time of coda part of S-waves and a one-dimensional crustal attenuation (Qs ) model characterized by weak attenuation and strong frequency dependence of Qs was obtained in 1-24 Hz. Next, radial receiver functions developed from teleseismic Pwaveforms of broadband seismographs at SYO in 1990-1993 were inverted for the crustal velocity models of shear waves, in which each layer's thickness was taken to be 1-2 km. Lateral heterogeneity was investigated by comparing the velocity models in the four backazimuth groups. Velocity changes were recognized as a sharp Moho at 36-38 km depth in the continental areas in 500-1600; in contrast we revealed smooth variation of crustal velocities together with transitional Moho in the bay backazimuths in 2100-360°. Continental velocity models in the two different facies terrains were also related to the linking velocity to lithology by laboratory data. In order to compare the shear wave crustal models with reflected waves in the crust, refraction data on the Mizuho Plateau were re-analyzed. The reflective layers are at depths of 24-45 km, which mainly correspond to the lower crust, with a well known relation to the Bouguer gravity anomalies. The Moho depth estimated from the Bouguer anomalies also indicated a seaward dipping Moho from 40 km in the coastal area to 48 km beneath Dome-F (77.4°S, 39.6°E). Crustal anisotropy for shear waves found by splitting analysis of Moho Ps phases was quantified by the fastest direction in N133°E, which is perpendicular to the upper mantle anisotropy from SKS phases. By comparing the crustal shear wave models with other geophysical and geological evidence, the reasonable crustal evolution in LHB is explained in relation with the regional metamorphism at 500 Ma and the last break-up of Gondwana at 150 Ma. 2
doi:10.11501/3117194
fatcat:gd6jo3aohvbevpdslvfk3jgujq