Subsidence assessment by 3D seismic surveying at Collingwood Park

Two subsidence events occurred at Collingwood Park on the 7 December 1988 and the 25 April 2008, respectively. Many houses were damaged in varying degrees by these events. The Queensland Government has taken these incidents seriously. In the interests of the wellbeing of the local community and through its Departments, the Government commissioned CSIRO to investigate the remedial treatments to control further surface subsidence in the suburbs that were undermined by the past underground coal mining activities. As part of the investigation, a 3D seismic trial survey was performed at Collingwood Park. The objective of the survey was to demonstrate the feasibility of 3D seismic surveying for identifying and locating subsurface structures and features such as faults and old mining workings. The seismic survey confirmed the location of the existing water line fault, and identified another normal fault. In addition, the seismic mapped subsidence zone is consistent with the observed subsidence on the surface. The failure area at the abandoned mining level is larger than the subsidence boundary at the surface. Post 3D seismic drilling confirms that the pillar failure extended beyond the water bearing fault.