The Effects of Local Structure upon Measurements of the Travel Time Gradient at the Warramunga Seismic Array

Measurements of dT/dΔ across the Warramunga seismic array are perturbed by variations in the structure beneath the array. On the assumption that the structure consists of uniformly dipping interfaces, an estimate of the effect was obtained by combining data from opposite azimuths. The results were not entirely satisfactory, however, because of the over-simplicity of the model. It seems likely that accurate array determinations of dT/dΔ can only be obtained by 'calibrating' the array, using events at distances for which dT/dΔ is already well known.