CODA ATTENUATION IN THE LUTZOW-HOLM BAY REGION, EAST ANTARCTICA

The frequency-dependent coda Q(c)-1 was estimated for the Lutzow-Holm Bay region, East Antarctica, on the basis of the single-scattering model, and discussed together with Q(c)-1 data of Kyoto, Japan, as an example of an active region. Coda waves from six shallow earthquakes, observed with a local telemetry seismic network installed along the Soya Coast, were analyzed with narrow band-pass filters. Q(c)-1 for a lapse time of 20-40 s was estimated to be 0.00495 f-0.776 for a frequency of 4-16 Hz, and Q(c)-1 for 150-210 s was 0.00335 f-0.926 for 1-24 Hz. In comparison with Q(c)-1 data for Kyoto and other regions with various tectonic conditions, Q(c)-1 in the Lutzow-Holm Bay region was characterized by large values at low frequency (around 1 Hz) and smaller values at higher frequency. From the single-scattering model, Q(c)-1 suggests a strong frequency dependence of intrinsic absorption for S waves. Assuming that the observed Q(c)-1 reflects scattering loss of energy, and taking account of the geological conditions and the extremely low seismic activity in the East Antarctic continental shield, it is suggested that the frequency-dependent Q(c)-1 is attributable to large scattering loss in the lower-frequency range caused by large-scale heterogeneities as a result of velocity and/or density perturbations.