The transfer of energy from water particle to water particle in the circular paths, or orbits, transmits wave energy across the ocean surface and causes the waveform to move. This kind of wave is known as an orbital wave which is a wave in that particle of the medium (water) move in closed circles as the wave passes. Orbital sea waves occur at the boundary between two media, between air and water and between layers of water of different densities. These waves are a type of progressive wave, because the waveform moves forward. Sea waves have distinct parts. The wave crest is the highest part of the wave above average water level; the wave trough is the valley between wave crests below average water level. Wave height is the vertical distance between a wave crest and the adjacent trough, while wavelength is the horizontal distance between two successive wave crests. The time it takes for two successive wave crests or troughs to pass a fixed point, usually measured in seconds, is known as the wave period. Wave frequency is the number of waves passing a fixed point per second. Frequency is the inverse of period. The circular motion of water particles at the surface of a wave continues underwater. Water particles move diminishes rapidly with depth. For all practical purposes, wave motion in deep-water waves is negligible below a depth of one-half the wavelength. Since most sea waves have moderate wavelengths, the circular disturbance of the ocean that propagates these waves affects only the uppermost layer of water.
Sea waves are classified by the disturbing force that creates them, the extent to which the disturbing force continues to influence the waves once they are formed, the restoring force that tries to flatten them, and their wavelength.
Energy that causes sea waves to form is called a disturbing force. Wind blowing across the sea surface provides the disturbing force for wind waves. Arrival of a storm surge or seismic sea wave in an enclosed harbor or bay, or a sudden change in atmospheric pressure is the disturbing force for the resonant rocking of water known as a seiche. Landslides, volcanic eruptions, and faulting of the seafloor associated with earthquakes are the disturbing forces for seismic sea waves which is also known as tsunami. The disturbing forces for tides are changes in the direction of gravitational forces among the Earth, moon, and sun, combined with Earth’s rotation.