seismographs [2]

Instruments that record seismic wave amplitude at a given point on the Earth’s surface.

horizontal seismograph

Instrument that measures 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.