Upper crustal seismic investigations of the Tennant Creek Block indicate that the Warramunga Group rocks have P-wave velocities of 5.22-5.55 km/s (average 5.42 km/s) and S-wave velocities of 3.26-3.41 km/s (average 3.34 km/s). The P-wave velocity beneath these surface rocks is 6.06 km/s. A simple layered model for the thickness of the Warramunga Group gives values of about 2.6 km near Nobles Nob mine, thinning to about 1.2 km near Warrego mine. South of the Warramunga Group rocks, granitic rocks have an estimated upper value for the P-wave velocity of 5.69 km/s. Underneath, the P-wave velocity of 6.06 km/s is the same as that further north, under the Warramunga Group rocks, but the depth to this velocity is as much as 0.7 km less. The corresponding S-wave velocity is 3.53-3.59 km/s. An intracrustal S-wave velocity of 3.86 km/s is observed from the Warrego shot. The nature of the change between the surface and basement rocks is likely to be complex, resulting in a velocity transition zone rather than a simple boundary. The estimated depths to basement are, therefore, minimum estimates. Because of the expected increase in the seismic velocity of the rocks when subjected to overburden pressures equivalent to depths of 2-3 km, there is little evidence from the present work that the basement is compositionally or lithologically different from the surface rocks. At recording distances beyond 50 km there is evidence in the record sections that both P and S-wave energy is being returned from deeper intracrustal refractors/reflectors.
