How Seismic is Collected

Seismic waves used to record seismic data are sound waves. They are generated by setting off a dynamite charge in small holes drilled into the surface or by using a hydraulic Vibroseis unit that physically strikes the ground. Dynamite is used for the majority of seismic recording in the WCSB because of its cost-effectiveness, its ability to record data from deeper formations and the compact size of the equipment, which enables heli-borne seismic surveying in environmentally challenging areas. Vibroseis is more common in the United States, where some jurisdictions restrict the use of dynamite, and is also practiced extensively in western Canada.

The stages of conducting a typical seismic survey in the WCSB are as follows:

1. Seismic lines or 3D grids are planned for a new area of interest. A ground survey is conducted to record the location and elevation of each seismic pulse source point (the places where the charges are set off or the Vibroseis impacts the ground) and receiver (the geophones where the sound wave data is recorded). The lines are spaced at intervals determined by the needs of the customer. Typical line spacing is 60 metres, but can vary from 20 metres to 100 metres. In addition to the "fold" of the data, very important is the care and attention taken in accurately placing the geophones, laying the lines and recording the seismic, resulting in "clean" versus "noisy" data.
   
   
2. Holes are drilled at the source points and charges are set. Vehicle-borne ground teams or heli-borne teams then lay down the seismic receiver lines at the pre-determined locations. Vehicle-borne teams require existing roads and land access, or entail cutting seismic corridors through forested areas. Modern practice is to use heli-borne teams in forested areas in order to minimize current environmental disturbance and longer-term impact. Today's compact equipment and low-impact practices leave behind minimal evidence of the seismic activity.
   
   
3. The charges are set off or the Vibroseis units operate at the source, generating sound waves that travel through the ground. The sound waves reflect off different types of rocks and travel at varying velocity through varying rock densities. This results in different time intervals for the various geological horizons. The returning sound pulses are captured by the geophones at the various time intervals, and the data is transmitted to a central data capture unit - the "dog house" in industry slang - where all the data is recorded onto a hard drive and then downloaded onto digital tapes.
   
   
4. Data is processed at an independent specialized provider. Following processing specialized software is used by the client's in-house geophysical department to interpret the data. In some cases, data is further refined into leading-edge 3D visualizations of the sub-surface geology.