What is a seismometer? What does it record?
A seismometer is a very sensitive instrument that can detect movements of the Earth’s surface. The surface is in constant motion due to natural and man-made phenomena. For example, the solid Earth tide is the stretching of the Earth due to the gravitational pull of the moon. Tucson slowly rises and falls twice a day about 40 cm due to the moon orbiting overhead. Mining explosions in Morenci, Arizona create seismic waves which shake Tucson daily. The amplitude of these vibrations are less than a micrometer and the oscillations have a frequency of several Hz. The wide variety of ground motion, both in terms of period of oscillation and amplitude of vibration make it impossible for a single seismometer to record all types of motion. The AS-1 seismometer is a simple inertial system that can detect local mining explosions as well as moderate or large earthquakes that occur globally. The seismometer is called inertial because it is based on Newton’s 1st Law: A body at rest will remain at res
