Application of passive seismic and AEM to 3D paleochannel imaging: Capricorn Orogen

Summary This study uses shallow passive seismic HVSR (horizontal-to-vertical spectral ratio) technique to determine the depth and extent of a Cenozoic paleochannel composed dominantly of sand and clay incised into the Proterozoic granitic basement of the Capricorn Orogen. The paleochannel contains sand-dominated intervals that host water that is presently being explored by Hastings Metals. There is some drilling data available but only a few drill cores intersect the basement. Improved understanding of the paleochannel geometry will assist with water exploration. The measured resonant frequency is related to shear wave velocity (Vs) and layer thickness. Passive seismic measurements at drill hole SWMB007 allow us to define a Vs for the regolith package overlying the basement. This Vs value is applied to 53 passive seismic measurements along Traverse 7 and the thickness of the paleochannel has been imaged in normalised H/V amplitude images. Along Traverse 7, HVSR data image a symmetrical paleochannel with a maximum depth of ~115 m. The geometry of the paleochannel imaged is broadly similar to the geometry obtained from 2.5D AEM inversion. However, the paleochannel has a greater maximum depth in AEM and some internal features of the paleochannel also differ.