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seismographs 
Instruments that record seismic wave amplitude at a given point on the Earth’s surface.
horizontal seismograph
Instrument used to measure horizontal ground movements.
seismogram
Graphic representation produced by a seismograph; the stronger the tremors, the greater the oscillations on the paper.
horizontal ground movement
rotating drum
Secured to the ground, it rotates under the pen, recording ground movements on paper.
mass
Independent of ground movement, it remains stationary during an earthquake, thus serving as a reference for measuring the amplitude of tremors.
pen
Writing instrument that converts ground movement into a line.
