Seismography
Seismography is the practice of measuring and recording ground motion produced by earthquakes and other sources, using seismometers and seismographs. It enables scientists to study the structure of the Earth and to monitor seismic hazards. An instrument typically consists of a mass suspended from a frame that is anchored to the ground; as the ground moves, inertia keeps the mass relatively still, and the relative motion is converted into a trace on a recording medium. Early systems used mechanical or electromechanical recorders; modern installations use digital sensors that sample at high rates and store data electronically.
Data are displayed as seismograms, showing waves such as primary (P) and secondary (S) waves, surface waves,
Seismographs fall into several classes, including short-period, long-period, and broadband devices, and they record vertical as