Trigger mechanisms and hydrodynamics of tsunamis

Tsunamis are mainly triggered by submarine earthquakes, but they are sometimes caused by landslides, volcanic activity, or the impact of extraterrestrial objects. Tsunamis caused by subduction-zone earthquake often generate ocean-wide impacts that affect the coastal environments in both near- and far-field regions. Recent studies have clarified additional mechanisms that enlarge tsunamis, such as seafloor uplift due to horizontal motion of the trench slope. Tsunamis triggered by landslides and volcanism are characterized by relatively small generation regions, short wavelengths, and high amplitudes. The generation processes and hydrodynamic characteristics of impact-induced tsunamis depend on the size of the impactor and the water depth of the target site. Tsunami propagation in the open ocean is described by the theory of linear long waves. Nonlinear effects become prominent in the nearshore zone due to shallow-water deformation. The hydrodynamic parameters of tsunami inundation, such as flow speed, have been measured using video records of recent events. Such data are beneficial to further exploration into the morphologic and sedimentologic role of tsunamis.