Seismogram

A seismogram is the record produced by a seismometer of ground motion caused by seismic waves. It is typically a time series of displacement, velocity, or acceleration, with time plotted on the horizontal axis and amplitude on the vertical axis. The exact quantity shown depends on the instrument and recording method.

Seismometers can be broadband or short-period, measuring motion along vertical and two horizontal components, and sometimes a fourth, or three components. Modern seismographs are typically digital and record traces on a computer or data center; older instruments used a mechanical pen on a rotating drum or photographic paper.

Seismograms display arrivals of seismic waves, including P-waves (compression), S-waves (shear), and surface waves. The relative arrival times and amplitudes help determine the distance to the source, direction, and often the magnitude of the event. They can be used in real-time monitoring and in post-event analysis.

Modern seismology relies on networks of seismometers to monitor regional and global seismicity. Seismograms are central data units for locating earthquakes, estimating their size, studying Earth's internal structure, and verifying compliance with nuclear-test moratoriums.