Gross crustal structure beneath northeastern Queensland from long-period P seismic data

Abstract

Crustal thickness and average seismic velocity can be determined by fitting the spectral ratio of the vertical and horizontal radial components of teleseismic long-period seismic P-waves to the theoretical spectral ratio of feasible crustal models. The vertical and horizontal radial transfer functions are calculated by the Haskell-Thomson matrix formulation pointwise in the frequency domain, by estimating the transmission coefficient of a given layered system for each of a sequence of input frequencies at the base. The character of the spectral ratios is affected mainly by the total crustal thickness and average velocity. Knowledge of these parameters is particularly valuable in combination with complementary data from deep crustal seismic reflections at near vertical incidence. Comparison tests using data from the ASRO/HGLP installation at Charters Towers (near the Queensland continental margin, Australia) reveal that the mean crustal thickness at Charters Towers is about 40 km and the mean Moho P-wave velocity contrast is 0.8. These values are consistent with independently derived models of 'normal' continental crust.