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seismographs 
Instruments that record seismic wave amplitude at a given point on the Earth’s surface.
vertical seismograph
Instrument that measures vertical ground movement.
vertical ground movement
bedrock
Extremely hard rock mass joined with the subsoil.
stand
Horizontal support that is secured to the ground.
pillar
Very solid vertical support.
mass
Independent of ground movement, it remains stationary during an earthquake, thus serving as a reference for measuring the amplitude of tremors.
spring
It keeps the mass from moving.
pen
Writing instrument that converts ground movement into a line.
rotating drum
Secured to the ground, it rotates under the pen, recording ground movements on paper.
seismogram
Graphic representation produced by a seismograph; the stronger the tremors, the greater the oscillations on the paper.
