SHEAR WAVE VELOCITY STRUCTURE IN THE CRUST AND UPPERMOST MANTLE BENEATH SYOWA STATION, EAST ANTARCTICA, USING MULTI-TRACE RECEIVER FUNCTION INVERSION OF BROAD-BAND TELESEISMIC WAVEFORMS

• Main Authors: カナオ マサキ, シブタニ タクオ, Masaki KANAO, Takuo SHIBUTANI
• Format: Report
• Language: English
• Published: National Institute of Polar Research 1995
• Subjects: East Antarctica; Syowa Station; Mizuho; Mizuho Plateau; Antarc*; Antarctica; Enderby Land
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2805; http://id.nii.ac.jp/1291/00002805/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2805&item_no=1&attribute_id=18&file_no=1

Receiver functions developed from teleseismic P-waveforms recorded on the broadband seismographs of Streckeisen seismometer (STS) at Syowa Station (69.0°S, 39.6°E), Enderby Land, Antarctica were inverted for vertical shear wave velocity structure beneath the station. By applying the source-equalization method (C. A. LANGSTON; J. Geophys. Res., 84,4749,1979), detailed observed receiver functions up to 100s from the P-arrival were obtained for total 32 earthquakes from May 1990 to January 1993 at three distinct back azimuths of 80°-90°, 140°-150°and 240°-250°. A time domain multi-trace inversion (T. SHIBUTANI; Ph. D. thesis, Kyoto Univ., Kyoto, 1993) was utilized for the radial receiver functions to determine the structure assuming a crustal model parameterized by many thin, flat-lying, homogeneous layers. Inversion was made after five-iterations by varying both velocity and thickness of the layers. The initial velocity model was adopted by Vp structure determined by the refraction experiments conducted in the northern Mizuho Plateau in 1979-1981 (A. IKAMI et al.; Mem. Natl Inst. Polar Res., Ser. C (Earth Sci.), 15,19,1984), with the constant poison ration of 1.73 in the crust and 1.80 in the uppermost mantle. Since the receiver functions are dominated by shear-converted phases, the inversion produces an estimate of shear wave velocity structure. The structure was sensitive for the layered thickness about 2 or 3km, corresponding to the small Gaussian high-cut filter coefficient of 2. Lateral heterogeneity is identified by examining azimuthal variations in the vertical structure. The rays from the back azimuth of 80°-90°and 140°-150°travel mainly in the continental area, on the contrary, the rays from 240°-250°samples the oceanic area. The result of 140°-150°has a gradual increase in the crust of the velocity from 3.0km/s to 3.9km/s. On the other hand, that of 240°-250°shows the existence of a high velocity zone in the upper crust (3.8km/s) and a low velocity layer in the mid-crustal depth. The result of 80°-90°has ...