By Jamie PoitrawGrade 9
Limestone Community School
A seismologist is a person who studies earthquakes and the mechanical characteristics of the earth. One aspect of seismology is concerned with measuring the speeds at which seismic waves travel through the earth. Seismologists also prepare seismic risk maps for earthquake-prone countries: these indicate the degree of seismic danger. In addition, seismologists use earthquake data to determine plate boundaries active earthquake areas generally coincide with plate margins, both destructive and growing, and transform faults. Instruments used to detect and record seismic disturbances are known as seismographs. Those in use today vary somewhat in design and function, but generally a heavy mass, either a pendulum or a large permanent magnet, is connected to a mechanical or optical recording device. When earthquake tremors occur, the pendulum or the magnet remains still as the earth moves. Three or more widely spaced seismographic stations are required to pinpoint the location of earthquakes.
Past earthquake studies have shown that P, or primary/compressional, waves travel fastest through the earth; S, or secondary/transverse, waves cannot pass through liquids, allowing scientists to discern the earth’s many boundary layers known as the crust, mantle and core.
An important commercial application of seismology is its use in prospecting for oil deposits. The first oil field was discovered by this method and was found in Texas in 1924. An explosive energy source is activated nearby; formerly, explosives such as dynamite, were used to create the seismic waves, but they have been largely replaced by high energy vibrators on land and air-gun arrays at sea. The waves generated are replaced by detectors known as geophones; on land, these are commonly placed in a fan-shaped pattern on the ground. From an interpretation of the waves created by the energy source and recorded by the seismograph, the detection of geological structures in which oil may be trapped is possible.
