Note that the methods scientists use to locate earthquakes on land and in the ocean are somewhat different.

On land, seismometers are used to measure the shaking of the ground from nearby earthquakes, but small earthquakes in the oceans are usually too far away to be detected.In the ocean, hydrophones are used instead to detect the faint rumbling sounds from oceanic earthquakes. Hydrophones are better for detecting oceanic earthquakes because sound waves (T-waves) travel much more efficiently in water than P- or S- waves do in the solid earth.

In addition, the difference in travel time between P- and S- waves can give the distance to an earthquake epicenter on land. In the ocean, however, only the acoustic T-wave is recorded so the travel time and earthquake epicenter must be calculated in a more complicated fashion from many observations. Hydrophone arrays can also give the direction to the epicenter, but cannot give any depth information.