Variations in the crustal structure of the Lutzow Holm Bay region, East Antarctica using shear wave velocity

Crustal structure in the Lutzow-Holm Bay region (LHB), East Antarctica, is studied by analyzing seismic waveforms derived from records in the vicinity of Syowa Station (SYO; 69.0 degrees S, 39.6 degrees E). One-dimensional crustal models for shear waves, in particular, are obtained in order to investigate crustal heterogeneity. Radial receiver functions developed from teleseismic P-waveforms of broadband seismographs at SYO in 1990-1993 are used in the time domain inversion, As the starting model in the receiver function inversion, a crustal attenuation model (Q(s)) for shear waves from local earthquakes of telemetry networks in 1987-1989 is derived by shifting the lapse time of the coda part of S-waves. Lateral heterogeneity is investigated by analyzing several backazimuth groups; namely the 50 degrees-100 degrees, 120 degrees-160 degrees, 210 degrees-250 degrees and 300 degrees-360 degrees sectors are investigated. Velocity changes are recognized as a sharp Moho at 36-38 km depth in the continental areas in the 50 degrees-100 degrees and the 120 degrees-160 degrees sectors; in contrast smooth variation of crustal velocities is revealed together with transitional Moho in the bay backazimuths in the 210 degrees-250 degrees and the 300 degrees-360 degrees sectors. In the continental backazimuths, a difference in crustal velocities is recognized between metamorphic terrain of granulite facies and the granulite-amphibolite transitional zone. Shear velocity models are compared with crustal reflectivity derived from the analysis of refraction data on the Mizuho Plateau. The reflective layers are found at depths of 24-45 km and appear to be related to the Bouguer gravity anomalies. By correlating the seismic models of crustal structure with other geophysical and geological evidence, the crustal evolution in LHB can be explained in relation to the regional metamorphism at 500 Ma and the last break-up of Gondwana at 150 Ma.