seismic

Seismic is an adjective relating to earthquakes and the motion of the Earth's crust, derived from the Latin seism-, meaning shake. In geology and geophysics, the term is used to describe phenomena, processes, and data associated with seismic activity, including earthquakes, seismic waves, and methods for monitoring and analyzing crustal vibrations.

Seismic waves originate at the earthquake source and propagate through Earth's interior and along its surface. They are classified as body waves, which include primary (P) waves that compress and expand the material, and secondary (S) waves that move material perpendicular to the direction of travel, as well as surface waves that travel along the crust and often cause ground shaking.

Seismology relies on instruments called seismometers or seismographs to record ground motion. Seismographs provide data used to determine the location, depth, and magnitude of earthquakes. Magnitude scales, such as the moment magnitude (Mw), quantify energy release, while intensity scales, like the Modified Mercalli Intensity (MMI), describe observed effects at specific locations.

Seismic hazard assessment evaluates the probability of ground shaking and its potential impacts, informing building codes, land use planning, and emergency preparedness. Seismic risk combines hazard with exposure and vulnerability. In some regions, early warning systems detect P-waves to provide seconds to minutes of warning before stronger shaking arrives, though warnings are not universally available.

Beyond natural earthquakes, seismic methods are used in subsurface exploration, such as seismic reflection surveys in geology and petroleum exploration, where controlled sources generate waves and recorded reflections reveal subsurface structures.