Tsunamis do not often come in one wave. They come as a group of waves which may turn a known coastline into a rush of water and debris before long, sometimes long after it was initially arrived at.
To the people who live on the coast, their safest weapon is the ability to recognize the warning signs of nature first, know what the official warnings are, and to be able to see something strange happening in the ocean as a signal to act instead of to observe.
1. Extensive, undulating shaking of the earth (20 seconds and above)
The duration of an earthquake may be an indication of the type of the seafloor movement that displaces a large amount of water. According to NOAA, a 20-second or longer long earthquake is one of the natural warning signs indicating the need to take immediate action in any tsunami prone region. The threat is not limited to the quake itself, the clock may tend to begin as soon as the shaking begins and particularly near subduction areas where the travel time of the tsunami can be very limited.
2. Squeezing like it knocks the people off their feet
It is not the duration but the intensity. The shaking of the ground that prevents standing can be an indication of strong ground movement in the near coast and the possibility of a locally incurred tsunami. In such cases, official notifications can also be received once the crucial decision has been made: the evacuation of low-lying regions has been left without any confirmation.
3. Ocean water soon recedes away to sea
When the sea suddenly and abnormally recedes, it may leave a few minutes later, rocks, seafloor and the stranded marine life. It is one of the most known tsunami precursors since it may occur prior to the first wave reaching the shore. A sudden and odd increase or decrease in the water level is a natural indicator of an approaching tsunami to NOAA.
4. The increase of ocean water is in a rapid manner that appears wrong
Not all tsunami express themselves with a retreat. At certain bays, harbors, and mouths of rivers, the initial change which may be observed is rapid and forcible inland movement, of water rising higher than usual, and passing over sides, and acting with an abnormality of velocity. Though the surface may appear to be an unsympathetic wave, the danger is what lies in the currents: the water which pushes in, turns back and pushes in once more through several hours.
5. A loud roar from the ocean
Most survivors report the presence of the deep continuous sound, not quite resembling a freight train, but rather the normal surf, just before the devastating movement of water approaches the coast. One of the natural signs in NOAA is the roar of the ocean. The sound may particularly be prominent at night, in fog or when the horizon is obscured, when visual information is delayed.
6. Sirens or an emergency warning signal, which does not coincide with the hazards of normal weather
In certain coastal societies, there are outdoor sirens and integrated broadcast systems that can be used to remind people to take orders at once. The attention signal of an imminent tsunami in the Oregon coast is a continuous tonal siren, which is three minutes long, then radio or television messaging. The danger is not in the sound noise but in its role as a time indicator that people living in the coastline must take as an indicator to cease normal operations and transition into an emergency state of mind.
7. A Tsunami Warning (and what it means by flood and current)
The official tsunami messaging is developed in such a way that it is supposed to be followed immediately, but the terms are easily misinterpreted. According to the National Weather Service, Tsunami Warning can be defined as follows:
a tsunami that could result in extensive flooding is approaching or occurring. It further says that there might be dangerous coastal flooding and strong currents that might last several hours or days after the first arrival. The fact that it is persistence that people fail to remember is common, particularly during those times when circumstances seem to be at ease between waves.
8. Headlong harbor and river streams which turn and turn again
The energy of a tsunami usually accumulates in avenues, such as marinas, inlets, and river mouths, in which the water can travel like a pumped stream. Strong currents or waves that are perilous to humans in or near deep water risk occur during a Tsunami Advisory, where floods of the beach and harbor may take place. The disturbing characteristic is the to-and-fro motion: water rushing in, emptying out, and back and forth, and even 12-24 hours on other guidance of planning of evacuation zones along the coastline.
Tsunami awareness is not the ability to remember melodramatic tales; it is the ability to identify patterns which have occurred over the centuries and along the coastlines. Natural indicators and government warning are also the same: they encourage early evacuation off the lowlands.
When the ocean is acting otherwise than it used to, and particularly when it has been shaken about, coastal safety is as easy as high priorities, keep out of danger areas, and wait till everything is all right instead of waiting till there is a lull.
