Tertiary wave in seismology introduced by Linehan(1940), next to P(primary) and S(secondary) waves. It is generated by an earthquake in or near the oceans, propagated in the oceans as an acoustic wave guided in the SOFAR channel and converted back to seismic wave at the ocean-land boundary near the recording site. See Kulhanek (2002) and Fig. 2.22 in Havskov and Ottemöller (2010)