Tsunami Warning 2
Tsunami Warning 2 : A tsunami warning is an alert, usually issued by a National Tsunami Warning Centre (NTWC), to indicate that a tsunami hazard is expected and imminent. A tsunami warning may be issued for different levels of tsunami threat. For example, a low-level threat is one characterized by small sea level changes and strong ocean currents, and the tsunami is only a hazard at beaches, in harbours, and for recreational ocean activities. During a major threat, high amplitude waves along with powerful currents can be expected and could cause significant inundation and complete destruction of most near-shore structures. Dangerous waves may continue for several hours after arrival of the initial wave. Different levels of warning should trigger different types of response by emergency officials and by the at-risk public. Appropriate public safety action taken when there is a major threat includes the evacuation of low-lying coastal areas, and the repositioning of ships to deep waters if there is time. Warnings may be updated, adjusted geographically, downgraded, or cancelled. To provide the earliest alert, initial warnings are normally based only on seismic information. Threat levels may be given different names by different countries depending upon their language and the standard nomenclature they use for other hazards such as weather events. In Japan, there are 66 coastal forecast regions, and warnings are issued specifically for each. There are three levels of threat based on the tsunami height forecast (major tsunami warning, tsunami warning, and advisory). JMA tsunami forecast regions (left) and 11 March 2011 Japan tsunami warning (top). The entire eastern coast of Japan was placed on alert 28 minutes after the M9.0 earthquake, with northern Japan under a Major Tsunami and the rest of the Pacific coast under a tsunami warning or advisory. All warnings and advisories were cancelled after 2 days, 3 hours and 12 minutes
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