Posted by: drazizul | January 14, 2010

Seismographs and Seismograms

seismograph

Sensitive seismographs are the principal tool of scientists who study earthquakes. Thousands of seismograph stations are in operation throughout the world, and instruments have been transported to the Moon, Mars, and Venus.
Fundamentally, a seismograph is a simple pendulum. When the ground shakes, the base and frame of the instrument move with it, but intertia keeps the pendulum bob in place. It will then appear to move, relative to the shaking ground.
As it moves it records the pendulum displacements as they change with time, tracing out a record called a seismogram.
One seismograph station, having three different pendulums sensitive to the north-south, east-west, and vertical motions of the ground, will record seismograms that allow scientists to estimate the distance, direction, Richter Magnitude, and type of faulting of the earthquake. Seismologists use networks of seismograph stations to determine the location of an earthquake, and better estimate its other parameters. It is often revealing to examine seismograms recorded at a range of distances from an earthquake:

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