microseism

Microseisms are small ground motions, distinct from earthquake waves, that are commonly recorded by seismographs. While they can complicate the accurate recording of earthquakes, microseisms are of scientific interest because their patterns relate to the Earth's surface structure.1

These subtle tremors can have local origins, such as traffic, machinery, wind effects, storms, or the action of surf against a coast. Another type of microseism appears similarly on seismographs worldwide, occurring simultaneously with similar amplitudes and frequencies, and can persist for hours with periods of five to eight seconds. These can be generated by large standing water waves far out at sea, with their periods being half that of the standing wave. The study of microseisms is known as microseismology.12