Undersea earthquakes make low frequency sounds from the movement of the seafloor. The sounds they make can be heard far away from the earthquake location. In the Pacific Ocean, sounds from a volcanic eruption have been heard thousands of miles away. Hydrophones located around the Pacific Ocean monitor the ocean for sounds of seismic events.Earthquakes produce acoustic signals known as T-waves. The T-phase duration and amplitude are related to the earthquake’s magnitude. Earthquakes produce acoustic energy in the 5 to 100Hz frequency range.