Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.See all posts »
Earthquake and Tsunami in Japan
Sendai Earthquake 2011
What to Do in an Earthquake
From my book Medicine for the Outdoors:
If you are caught in an earthquake in a wilderness setting, do the following:
1. Seek a safe location, out of the path of a rockfall, mudslide, or snow avalanche. If you can, move into a clearing away from buildings, trees, and power lines. If the ground shaking is extreme, position yourself on your hands and knees.
If you are in a moving vehicle, drive to a clearing, exit the vehicle and stay next to it until the shaking stops. If something collapses upon it while you are inside, you may be crushed. If you are outside the vehicle, it may compress and create a safe space adjacent to it.
If you are indoors, stay put until you are certain that it’s safe to go outside. Move away from glass windows. Curl into a fetal position, and position yourself next to something that can compress, but not crush, and thereby protect you by leaving an adjacent void. If you are in a bed during an earthquake, roll off the bed and remain next to it. Do not remain in a doorway and try to stay off stairs.
2. Eliminate any obvious fire hazards. If you are in a cabin supplied with natural gas, turn it off at the source if there is any odor or you believe there might be a leak.
3. Be prepared for aftershocks.
4. Secure a supply of drinking water. Be certain that you are prepared for a period of time without electrical power.
5. Prepare a shelter, store sufficient food, and locate equipment necessary for survival. Keep first-aid supplies and a flashlight within easy reach.
From the chapter entitled “Natural and Human-Made Hazards” by Sheila B. Reed in the 5th edition of the textbookWilderness Medicine:
Tsunami is a Japanese word meaning “harbor wave.” Although tsunamis are sometimes called “tidal waves,” they are unrelated to the tides. The waves originate from undersea or coastal seismic activity, landslides, and volcanic eruptions. They ultimately break over land with great destructive power, often affecting distant shores.
The geologic movements that cause a tsunami are produced in three major ways. The foremost cause is fault movement on the sea floor, accompanied by an earthquake. The second most common cause is a landslide occurring underwater or originating above the sea and then plunging into the water. A third cause of a tsunami is volcanic activity, which may uplift the flank of the volcano or cause an explosion.
Tsunamis differ from ordinary deep ocean waves, which are produced by wind blowing over water. Normal waves are rarely longer than 300m (984ft) from crest to crest. Tsunamis, however, may measure 150km (90 miles) between successive wave crests. Tsunamis travel much faster than do ordinary waves. Compared with normal wave speed of around 100kph (62mph), tsunamis in the deep water of the ocean may travel at the speed of a jet airplane - 800kph (497mph). Despite their speed, tsunamis increase the water height only 30 to 45cm (12 to 18 inches) and often pass unnoticed beneath ships at sea.
Contrary to popular belief, the tsunami is not a single giant wave. A tsunami can consist of 10 or more waves, termed a tsunami wave train. The waves follow each other in 5- to 90-minute intervals. As tsunamis approach the shore, they travel progressively slower. The final wave speed depends on the water depth. Waves in 18m (59ft) of water travel about 50kph (31mph). The shape of the near-shore sea floor influences the behavior of tsunami waves. Where the shore drops off quickly into deep water, the waves are smaller. Areas with long shallow shelves, such as the major Hawaiian islands, allow formation of very high waves. In the bays and estuaries, seiches where the water sloshes back and forth can amplify waves to some of the greatest heights ever observed.
Tokyo After the Earthquake
The flooding produced by a tsunami may vary greatly from place to place over a short distance, depending on submarine topography, shape of the shoreline, reflected waves, and modification of waves by seiches and tides. The sequence of the largest wave in the tsunami wave train also varies, and the destructiveness is not always predictable.
Tsunamis have occurred in all oceans and in the Mediterranean Sea, but the majority of them occur in the Pacific Ocean. The zones stretching from New Zealand through East Asia, the Aleutians, and the western coasts of the Americas all the way to the South Shetland Islands are characterized by deep ocean trenches, explosive volcanic islands, and dynamic mountain ranges.
A tsunami is almost always generated by an undersea earthquake of magnitude 7 or greater. Therefore, special warning alarms sound when a quake measuring 6.5 or more occurs anywhere near the Pacific. A tsunami watch is declared if the epicenter is close enough to the ocean to be of concern. Government and voluntary agencies are then alerted, and local media are activated to broadcast information. The five nearest tide stations monitor their gauges, and trained observers watch the waves. With positive indicators, a tsunami warning is issued.
The following major factors contribute to vulnerability to tsunamis:
- Growing world population, increasing urban concentration, and larger investments in infrastructure, particularly on the coastal regions, with some settlements and economic assets on low-lying coastal areas
- Lack of tsunami-resistant buildings and site planning
- Lack of a warning system or lack of sufficient education for the public to create awareness of the effects of a tsunami
- Unpredictable intensity
The force of water in a bore, with pressures up to 10,000kg/m2, can raze everything in its path. The flooding from a tsunami, however, affects human settlements by water damage to homes, businesses, roads, and infrastructure. Withdrawal of the tsunami also causes significant damage. As the water is dragged back toward the sea, bottom sediments are scoured out, collapsing piers and port facilities and sweeping out foundations of buildings. Entire beaches have disappeared, and houses have been carried out to sea. Water levels and currents may change unpredictably, and boats of all sizes may be swamped, sunk, or battered.
Deaths occur principally from drowning as water inundates homes or neighborhoods. Many people may be washed out to sea or crushed by the giant waves. Some injuries occur from battering by debris. Little evidence exists of tsunami flooding directly causing large-scale health problems. Malaria mosquitoes may increase because of water trapped in pools. Open wells and other groundwater may be contaminated by salt water and debris or sewage. Normal water supplies may be inaccessible for days because of broken water mains.
Finally, my good friend Eric Noji, MD has suggested following this link to a lecture on tsunamis with educational material for all persons concerned with tsunamis, their effects, and disaster mitigation:
Adapted from the title page of the lecture:
“This lecture is dedicated by the Global Health Disaster Network (GHDN) to the victims of the 26 Dec 2004 disaster in South Asia. We wish to help save the affected people and to prevent more mortality and morbidity by providing a scientific understanding of tsunamis.”
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