In preparing to write my novel Tsunami, about a fictional undersea volcano on the verge of exploding and sending a monster tsunami smashing into California, I did a great deal of research into the world of natural disasters. I leaned heavily on NOAA, USGS, NASA and dozens of library and university sources for my information. One thing became clear as I dug into the research: tsunamis are not self generating. They are always the product of some other natural event.
Tsunami - a seismic sea wave - means in Japanese "harbor-wave". It is also misleadingly called "tidal wave". It is an ocean wave caused by an earthquake of magnitude 6.5 on the Richter scale (or greater) that occurs less than 50 kilometers beneath the seafloor. Tsunamis can also be caused by volcanic eruptions and by landslides.