There is growing interest in using geophysical information from a variety of sources for resource exploration and management. As the search for raw materials becomes more difficult, future discoveries are likely to be deeper and concealed under sediment cover. Incorporation of information from many methods will become crucial to future exploration programs. Additionally, deep geophysical methods specialising in imaging the region from basement to full crustal depth will provide key geophysical constraint – an area where conventional methods are lacking.
Odyssey Geophysics is a leader in delivering deep passive geophysical methods – namely passive seismic methods – that are sensitive to deep crustal structure.
Passive geophysical methods, as opposed to active source methods, measure signal from natural Earth phenomena to image the sub-surface. This has a major advantage over active methods, namely that passive sources are readily available and at no cost. For example, passive seismic methods can utilise energy across a very broad frequency range, this can include ocean waves crashing on distant shorelines, wind through a forest, micro tremors and earthquakes on the other side of the globe.
Additionally, passive sources often illuminate crustal structure from angles impossible to obtain using conventional active sources. An example is seismic earthquake energy travelling from a distant epicentre, through the interior of the Earth, and then propagating from the base of the crust to a recorder on the surface. Energy travelling along this path certainly has a different experience of deep crustal structure! This information helps to constrain the characteristics of geological structure and lithologies present.
The key to passive geophysics is unravelling the signal of interest, i.e. for resource exploration: signals originating from crustal structure. This can be difficult as the source timing and other characteristics may be unknown – which is not the case for active sources.
An Odyssey Geophysics vision for Passive Seismic Geophysics:
With the continued advancement in modern technology and easy access to computer power. Passive seismic for resource exploration will continue to gain momentum. With high density seismograph arrays, information on local structure to full-crustal depth can be gathered cheaply and efficiently. The same instrumentation can then be utilised for large regional scale arrays to understand the tectonic history of an area.
Ongoing development of processing and inversion algorithms will facilitate high-resolution passive seismic models. The proliferation of on-the-ground seismographs will greatly enhance passive seismic studies, as information from local stations can be combined with permanent networks to enhance the usefulness of temporary station data.
Some exciting areas of innovation include:
- Imaging of deep crustal, including Moho structure. Improving receiver function and seismic tomography workflows.
- Shallow (to basement) methods such as HVSR – quicker and more robust processing and inversion algorithms.
- Joint inversion of different passive seismic techniques, i.e. Receiver Function (deep) and HVSR (basement) joint inversion
- Full waveform inversion (FWI) for more detailed imaging
- Smaller broadband seismometers – allowing quicker deployments but still offering cutting edge sensitivity
- High capacity, lightweight batteries – reducing the size and weight of the systems for faster deployment
Odyssey Geophysics has the skills, expertise and drive to spearhead innovation in these areas, bringing passive seismic geophysics into the future.