Seismic spectrum

Studies of earth-quakes typically use the period range from approximately 0.1 s to more than 3000 s, or frequencies from 10 Hz to 0.3 mHz. Higher-frequency waves of 20 - 80 Hz generated by explosions or other artificial sources are used in reflection seismology to explore the earth's crust. Still higher frequencies, 3 - 12 kHz, propagating primarily in the ocean, are used by marine geophysicists to map the sea floor. At the other end of the spectrum, ground motions with periods longer than 10 ksare due to slow crustal motions rather than propagating seismic waves.