Chapter 2 - Tsunami Generation and Historical Aspects

Abstract

This chapter reveals that both tsunamis and tsunami-like waves are generated as a result of various causes, such as an undersea earthquake (also known as a seaquake) rupture process or, more frequently, the secondary triggered phenomena, such as landslides and/or other geodynamic phenomena, such as rockslides, large-scale gas emissions from the seafloor, volcanic eruptions, intense atmospheric disturbances, and asteroid impacts. According to the tsunami database, seaquakes, submarine landslides, volcanic eruptions, and atmospheric disturbances have been responsible for approximately 82%, 6%, 5%, and 3%, respectively, of tsunamis. Most of the historic seaquakes (i.e., earthquakes under the seafloor) have taken place at subduction zones. The presence of a deep-water trench, such as the Aleutian trench in the Alaska-Aleutian subduction zone and the Kuril-Kamchatka trench in the Kuril-Kamchatka zone, is the main characteristic of the subduction zone. The depth at the trench axis is approximately twice as large as an average depth of the Pacific Ocean. Earthquake hypocenters are mainly located under the continental bottom slope. In this case, the opposite slope of this deep-water trench works like an optical lens for tsunami waves.