A thumper truck is a vehicle-mounted system for generating seismic vibrations and is used primarily by seismologists and geophysicists to locate and measure deposits of oil and natural gas. Thumper trucks are only one of several methods used to generate seismic data for this purpose, but they are the fastest, most efficient and least dangerous.
Large and rugged, the thumper truck is designed for use in areas of difficult, often hilly terrain. It carries a heavy ground-impact weight which is raised by a hoist to a height of approximately nine to ten feet (2.7 to 3.04 m). The weight is then released to “thump”, or impact, the ground. Geophones, positioned to receive the seismic signal from the impact of the weight, then transmit the data to measuring instruments located in a recording vehicle nearby. This seismic information is often augmented by a series of impacts, either in the same spot or in several different locations nearby. This series of “thumps” is arrayed to enhance the quantity and accuracy of the data.
Though somewhat destructive in its own right, a thumper truck is far less environmentally devastating than dynamite, which, for some time, was the preferred method for the generation of seismic signal data. Dynamite is, by its nature, inherently dangerous to use. It is also ecologically devastating in that it necessitates the digging of “shot-holes” which are then expanded by the explosive into sizeable craters. This uncontrolled force can cause severe ecological damage over a much wider area than does a thumper truck.
These vehicles maintain one further advantage over the use of dynamite in seismic data generation. They are a far less threatening exploration technique in areas of political instability than is any sort of explosive.
The thumper truck generates seismic data through a single impulse – the singular release of the weight. Vibroseis, a vehicle-mounted hydraulic vibrator, also known as a shaker unit, provides seismic signals over a longer time period, thus data is continuous as opposed to interrupted. Vibroseis vehicles are somewhat easier on the soil, as well. Specialized air guns and plasma sound sources (PSS), sometimes called spark gap sound sources, though less destructive than dynamite or a thumper truck, are not quite as accurate or as efficient.
Any exploration of natural deposits will be environmentally damaging to an extent. The use of a thumper truck is no different. USGS scientists estimate that the soil damage occasioned by the constant dropping of its impulse weight in a relatively constricted testing arc, especially along ridgelines, could take decades to rectify.