seismographs [2]![click to hear](/images/speaker.jpg)
Instruments that record seismic wave amplitude at a given point on the Earth’s surface.
horizontal seismograph ![click to hear](/images/speaker.jpg)
Instrument that measures horizontal ground movements.
seismogram ![click to hear](/images/speaker.jpg)
Graphic representation produced by a seismograph; the stronger the tremors, the greater the oscillations on the paper.
horizontal ground movement ![click to hear](/images/speaker.jpg)
rotating drum ![click to hear](/images/speaker.jpg)
Secured to the ground, it rotates under the pen, recording ground movements on paper.
mass ![click to hear](/images/speaker.jpg)
Independent of ground movement, it remains stationary during an earthquake, thus serving as a reference for measuring the amplitude of tremors.
pen ![click to hear](/images/speaker.jpg)
Writing instrument that converts ground movement into a line.