The Collaborative International Dictionary
Seismic vertical
Seismic \Seis"mic\, Seismal \Seis"mal\, a. [Gr. seismo`s an earthquake, from sei`ein to shake.] Of or pertaining to an earthquake; caused by an earthquake.
Seismic vertical, the point upon the earth's surface vertically over the center of effort or focal point whence the earthquake's impulse proceeds, or the vertical line connecting these two points.