本文
When an earthquake occurs under the seafloor, the seafloor rises and sinks, and the overlying water is rapidly pushed up and down over a wide area in a short period of time. This causes a great rise and fall of the sea surface, generating a series of waves which turn into tsunami waves.
Fault movement (earthquake) under the seafloor causes crustal deformation, pushing up the overlying water. This mass of uplifted water produces tsunami waves which spread out in all directions in the sea.
Wind waves are a phenomenon produced by winds blowing over the sea, and occur near the sea surface. Their wavelength (the length between wave crests or troughs) ranges from several meters to hundreds of meters.
Meanwhile, a tsunami is the propagation phenomenon of sea waves produced as a consequence of the rise and fall of the sea surface that are generated when the seafloor is deformed by an earthquake or other seismic activity, vertically displacing the overlying water over a wide area of sea in a short period of time. The wavelength of a tsunami is very long, from several kilometers to hundreds of kilometers. This means that massive amounts of water welling up from the seafloor to the surface sweep into coastal areas.
Tsunami waves hit coastal areas repeatedly without losing their power, and rise up to a higher elevation than themselves at the coast. Tsunami waves also suddenly become higher when approaching a shallow coast. Moreover, when they recede, they continue receding for a long period of time, maintaining their strength. Accordingly, damaged houses and other floating objects are pulled into the sea all at once.
(Source: Website of the Japan Meteorological Agency)
When an earthquake occurs, the Japan Meteorological Agency promptly estimates its size and location, and based on these, calculates how high the tsunami will be at the coast to announce a major tsunami warning, a tsunami warning, or a tsunami advisory within approximately three minutes after the occurrence of the earthquake.
Even if a tsunami occurs, you can potentially reduce the damage it causes if you respond quickly and evacuate early. To stay safe from a tsunami, please follow the five tips below:
In principle, when a tsunami advisory, tsunami warning, or major tsunami warning is announced by a meteorological observatory, the city will issue an evacuation notice to areas requiring evacuation.
Source: Report for Anticipated Damage from an Earthquake in Hiroshima Prefecture (October 2013)
Supervisory authorities responsible for developing coastal and river banks in the city are shown on the map. For the status of development, please contact the individual supervisory authorities.
Disaster Prevention Division, Crisis Management Office
1-6-34 Kokutaiji-machi, Naka-ku, Hiroshima
Tel: 082-504-2664 // Fax: 082-504-2802
Email: saigaiyobo@city.hiroshima.lg.jp