Today's photo is of a seismic vibrator – a Failing Y1100 on a birdwagen Mark III hydraulic 4-wheel drive buggy.
The vibrator is the piece in the middle. It has a pad in contact with the ground and above that, hidden in the chassis of the vehicle, a hydraulicly powered mass. On a start signal from the recording truck, the electronic controller would cause the mass and pad to vibrate through a known series of frequencies.
The sound waves would travel down into the ground and get refracted at various rock density transitions and get echoed back to the surface where the vibrations would be detected by geophones and their signals recorded. Correlating the echoes coming back with the sweep put in would, through the magic of maths and computers, result in sections through the earth showing the major rock layers. Certain rock formations form traps for oil and gas so reading the seismic sections along with other inputs helps a geophysicist know where to site a well for a better than average probability of finding oil or gas.
It's not foolproof though as the oil or gas might have migrated in the millenia after the traps were formed, and there may never have been any organic matter below the trap to start with.
The ‘birdwagen' was named after the founder of Industrial Vehicles International, Inc., James M. Bird of Tulsa, Oklahoma. The hydraulic drive had no transmission, no transfer case, no universal joints, no differentials or axles. Instead, each wheel had its own hydraulic motor.
To give you an idea of the scale, the tires are about 60 inch (1.5 m) diameter.
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