Shear velocity structure beneath the Western Australian region

Single station group velocities for Rayleigh and Love waves in the period range 20–70 s have been derived for twelve propagation paths between the digital seismic station at Narrogin (NWAO) in Western Australia and events in the Bali to the Timor region. The group velocity dispersion separates into two distinctive sets. The first set, with azimuth between 193–203° (eastern paths), samples only the Western Australian continent, while the second set, with azimuth between 174–180°, samples 65% of the Western Australian continent together with 35% of the North Australian Basin (that part of the deep ocean of depth greater than 4 km between the northern part of Western Australia and Bali). The inversion of velocity dispersion of the eastern paths for shear velocity‐depth structure shows that a 40 ± 2.5 km thick crust needs an S‐velocity of 4.20 ± 0.05 km/s for the lower crust, and an increase in S‐velocity from 4.48 ± 0.07 km/s at the Moho to 4.7 ± 0.3 km/s at 320 km depth. The inversion of North Australian Basin Rayleigh wave group velocities, obtained by decomposition of velocities in the second set, shows a very thin crust, about 4 km thick, and a high S‐velocity, 4.7 km/s, for the uppermost mantle. This result is preliminary as the data are limited.

Key words:

• crust
• North Australian Basin
• seismic waves
• upper mantle
• Western Australia