seismograms

Seismograms are records of ground motion captured by seismometers during earthquakes and related events. The instrument detects vibrations of the Earth and converts them into a time series, typically displayed as displacement, velocity, or acceleration over time.

Most modern stations record three components of motion: vertical, north-south, and east-west. These traces may be recorded digitally and stored for later analysis. Some stations also measure rotational motion, but standard three-component sensors are most common.

Interpretation: Seismograms show the arrival of different seismic waves. P-wave onset is the first fast arrival, followed by S-waves and surface waves. The relative sizes and shapes of the waveforms help estimate the magnitude of the source, locate its epicenter using arrival times at multiple stations, and infer properties of the Earth's interior along the path. Seismograms are also used to monitor non-tectonic sources and to study structural response of buildings, oil reservoirs, and other targets.

Data handling: to compare traces across stations, instrument responses must be removed or deconvolved to yield true ground motion. Traces are filtered, and magnitudes are computed using modern scales such as moment magnitude rather than older displacement-based measures. Seismograms form the basis of seismology's networks, including global and regional arrays that feed agencies like USGS and IRIS.

History: Seismographs were developed in the late 19th century and have evolved into highly sensitive, digital broadband instruments that can record a wide range of frequencies and amplitudes.