Seismic

The seismic survey technique is the principal geophysical method used in Australia to acquire images of the Earth’s crust at depth which provides data on its structure and its resources. Geoscience Australia has recognised the importance of the seismic technique since the late 1940s and is a world leader in integrating seismic data with other Earth imaging and surface geology datasets to understand mineral systems. Geoscience Australia routinely acquires seismic data to gather new pre-competitive data in Australia’s unexplored onshore and offshore frontier regions as well as obtaining additional regional seismic datasets in already explored regions of Australia known to have petroleum, geothermal or mineral potential.

Seismic Results

Seismic studies often are a major component of most geological projects within Geoscience Australia and are an essential part of any Geoscience Australia project involving investigating the Earth at depth.

Over the years, Geoscience Australia has acquired many kilometres of seismic reflection data across Australia's onshore and offshore regions and many more are needed to develop a complete understanding of Australia's geology and its hydrocarbon and mineral resources potential.

Example of interpreted seismic reflection

Example of interpreted seismic
reflection
© Geoscience Australia

As part of the Australian Government's 2007-2011 Energy Security Initiative, Geoscience Australia will acquire in excess of 4000 kilometres of additional onshore seismic reflection data and in excess of 12 000 kilometres of additional offshore seismic reflection data as part of a series of specifically targeted projects looking at Australia's frontier regions. These data are being used to provide fundamental datasets to assist in the ongoing evaluation of Australia's hydrocarbon, minerals energy and geothermal resources.

In addition to the ongoing collection of seismic data, Geoscience Australia reprocesses selected lines within the existing seismic reflection data held in its repository and uses newer and more advanced processing techniques to improve the final seismic image.

Map of offshore seismic lines from 2003-11

Map of offshore seismic lines from
2003-11
© Geoscience Australia

Two recent examples of Geoscience Australia seismic reflection surveys include:

  • The 2006 Isa-Georgetown-Charters Towers Seismic Survey acquired in excess of 1400 kilometres of onshore seismic reflection data across little explored regions of northern Queensland seeking information on the hydrocarbon, minerals energy and geothermal resources across the region.
  • The 2008-09 Southwest Margins Seismic Survey acquired approximately 7300 kilometres of offshore seismic reflection data along Western Australia's continental margin to provide fundamental pre-competitive data and information to understand these offshore frontier basins and assist with planning and management of Australia's marine environments. The data will support ongoing assessments also of the petroleum potential of these sedimentary basins.

Seismic Methods

There are two main types of seismic data, seismic reflection and seismic refraction. The seismic reflection method records signal reflected from geological strata below while the seismic refraction method records signal refracted along the geological strata.

Schematic diagram showing difference between seismic reflection and seismic refraction

Schematic diagram showing
difference between seismic
reflection and seismic refraction
© Geoscience Australia

Seismic reflection methods are the most common worldwide and are used extensively by the petroleum industry to explore, discover, delineate and monitor hydrocarbon resources in both onshore and offshore areas in a wide variety of environments. Seismic reflection results provide high-resolution, high-detail structural images of the subsurface of the Earth’s crust. The seismic reflection method can be scaled up or down to focus on:

  • near surface targets such as groundwater channels, regolith profiles, palaeochannel mineral-energy resources and mine structure
  • deeper targets such as hydrocarbon reservoirs, carbon capture and geological storage sites and geothermal deposits
  • crustal scale targets such as crustal structure, whole-of-mineral-system, major fault systems.

Geoscience Australia has successfully used the seismic reflection technique in all these areas.

The equipment used for acquisition of seismic reflection data is different for onshore and offshore exploration. For acquisition of seismic reflection data onshore seismic waves which are similar to sound waves are generated by Vibroseis trucks. These machines are essentially large hydraulic vibrators mounted on trucks and are about the size of a standard prime mover.

The resulting seismic waves travel down through the Earth and are reflected, or echoed off horizons deep within the Earth. These reflected echoes are detected by an array of geophones, which are similar to sensitive microphones and positioned at specific distances at the surface. The recorded signals are later processed to produce an image of the subsurface geology.

For acquisition of seismic reflection data offshore the energy source which creates the seismic waves is generated by an acoustic airblast released below the sea surface.

Seismic refraction methods are less commonly used in energy exploration but are a fundamental component of most geohazard research, including earthquake investigations, tsunami detection and warning systems and for monitoring nuclear explosions.

Geoscience Australia has, and will continue to use seismic refraction techniques for energy exploration because of its application in determining potential lithology and temperature, which are two key parameters in understanding the deeper structure and likely constraints on hydrocarbon potential.

Topic contact: minerals@ga.gov.au Last updated: October 4, 2013