Subsidence Assessment Using 3-D Seismic Data at Collingwood Park, Brisbane

Abstract

A 3-D reflection seismic trial survey was conducted at Collingwood Park, on the outskirts of Brisbane, Australia, where coal mining activity ceased in the 1980’s and two subsidence events occurred in 1988 and 2008. The objective of the survey was to demonstrate the feasibility of using seismic methods to locate subsurface structures and features such as faults and old mining workings. In spite of the strong contamination of refractions and surface waves, the survey was able to confirm the location of the previously known Waterline fault, as well as identify another fault. It accurately delineated the subsidence zone based on differences in the amplitude of seismic reflections from the surveyed area, and mapped the surface subsidence boundary, which correlated well to existing data from observations in the field. In addition, the seismic data were used to map the failure boundary at the seam level in relation to the subsidence zone. It was found that the mapped area at the seam level was larger than the surface subsidence boundary, with an estimated angle of ~21° between the subsidence failure surface and the vertical depth axis, depending on location. Post 3-D seismic drilling also confirmed that pillar failure extended beyond the Waterline fault. However, the survey failed to image the mine workings because of insufficient seismic resolution. To our knowledge, this is the first report on the use of 3-D seismic surveying to map deeply buried mining-related geotechnical failure boundaries.