Abstract
Summary Over six hundred values of the P wave travel-time gradient (dT/dΔ) and azimuth have been derived from 224 events recorded at the Warramunga Seismic Array over the teleseismic distance range 28° to 99°. These data show azimuthally dependent systematic errors which have been analysed on a regional basis and shown to be produced largely by lateral variations in the structure of the upper mantle beneath the array and complex topography near the base of the crust. The systematic changes in waveform of the P arrivals and curvature of the wavefront across the array observed in some azimuth ranges are probably due to the irregularities at the base of the crust. In addition, over one hundred dT/dΔ and azimuth measurements have been made for both first and second arrivals from 45 events over the distance range 13° to 28°. Systematic errors in these parameters have been examined in relation to lateral variations in structure both along the whole of the transmission path and close to the deepest points of the ray paths. The usefulness of array dT/dΔ measurements in refining our knowledge of Earth structure has been assessed in the light of recent developments in plate tectonics and evidence for regional variations in mantle structure.
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