Several well-known tomographic studies published in the 1990's (van der Hilst et al., 1991; Fukao et al., 1992) captured a large-scale subhorizontal high velocity anomaly at the bottom of the upper mantle in the northwestern Pacific. These models suggest that a large volume of subducted slab is stagnant in the transition zone.
On July 17, 1998, three huge waves – "tsunamis" – up to 15 meters high struck the north coast of Papua New Guinea, killing at least 2,200 people. A major earthquake, itself consisting of waves traveling through the Earth, triggered an underwater landslide that created the tsunamis. Radio stations reported the disaster by transmitting electromagnetic radio waves to listeners around the world. Listeners were able to hear the news transported by sound waves created by their radios.