Shallow marine investigations in Australia with advanced underwater seismic refraction (USR)

Abstract

Underwater seismic refraction (USR) with advanced interpretation approaches makes important contributions to shallow marine exploration and geotechnical investigations in Australia?s coastal areas. We present a series of recent case studies to demonstrate the application of continuous and static USR methods to river crossing and port infrastructure projects around Australia. In Sydney, static USR and borehole seismic imaging assisted the development of improved geotechnical models that reduced construction risk for a tunnel crossing of the Lane Cove River. In Victoria, combining conventional boomer seismic reflection and continuous USR improved the definition of a submerged, buried basalt flow and dredging assessment for navigation channel upgrades at Geelong Ports. Sand quality assessment with continuous USR and widely spaced borehole information led to improved commercial decisions on available sand resources for the reclamation phase of development at the Port of Brisbane. Buried reefs and indurated layers occur in Australian coastal sediments with the characteristics of laterally limited, high velocity, cap layers within lower velocity materials. If these features are not recognised then significant error in depth determination to deeper refractors can occur. Application of advanced seismic refraction inversion using wavefront eikonal tomography and continuous USR data obtained along the route of a proposed offshore pipeline near Fremantle allowed these layers and the underlying bedrock refractor to be accurately imaged. Static USR and the same interpretation approach was used to image the drowned granitic regolith beneath sediments and indurated layers in the northern area of Western Australia at a proposed new berthing site where deep piling was required. This accurately mapped the regolith and identified preferred piling sites that minimised pile lengths. USR can be expected to find increased application to shallow marine exploration and geotechnical investigations in Australia?s coastal areas as economic growth continues.