What are tsunamis?
2011/03/13 01:26:01 (UTC)
Preliminary Magnitude: 6.6
Latitude: 35.605 Longitude: 142.038
Location: off the east coast of Honshu, Japan
Tsunamis are large ocean waves generated by major earthquakes beneath the ocean floor or major landslides into the ocean. Tsunamis caused by nearby earthquakes may reach the coast within minutes. When the waves enter shallow water, they may rise to several feet or, in rare cases, tens of feet, striking the coast with devastating force. People on the beach or in low coastal areas need to be aware that a tsunami could arrive within minutes after a severe earthquake.
The tsunami danger period can continue for many hours after a major earthquake. Tsunamis also may be generated by very large earthquakes far away in other areas of the ocean. Waves caused by these earthquakes travel at hundreds of miles per hour, reaching the coast several hours after the earthquake. The International Tsunami Warning System monitors ocean waves after any Pacific earthquake with a magnitude greater than 6.5. If waves are detected, warnings are issued to local authorities who can order the evacuation of low-lying areas if necessary.
Why prepare for tsunamis?
All tsunamis are potentially, if rarely, dangerous. Twenty-four tsunamis have caused damage in the United States and its territories in the past 200 years. Since 1946, six tsunamis have killed more than 350 people and caused significant property damage in Hawaii, Alaska, and along the West Coast. Tsunamis have also occurred in Puerto Rico and the Virgin Islands.
When a tsunami comes ashore, it can cause great loss of life and property damage. Tsunamis can travel upstream in coastal estuaries and rivers, with damaging waves extending farther inland than the immediate coast. A tsunami can occur during any season of the year and at any time, day or night.
How can I protect myself from a tsunami?
If you are in a coastal community and feel the shaking of a strong earthquake, you may have only minutes until a tsunami arrives. Do not wait for an official warning. Instead, let the strong shaking be your warning, and, after protecting yourself from falling objects, quickly move away from the water and to higher ground. If the surrounding area is flat, move inland. Once away from the water, listen to a local radio or television station or NOAA Weather Radio for information from the Tsunami Warning Centers about further action you should take.
Even if you do not feel shaking, if you learn that an area has experienced a large earthquake that could send a tsunami in your direction, listen to a local radio or television station or NOAA Weather Radio for information from the Tsunami Warning Centers about action you should take. Depending on the location of the earthquake, you may have a number of hours in which to take appropriate action.
What is the best source of information in a tsunami situation?
As part of an international cooperative effort to save lives and protect property, the National Oceanic and Atmospheric Administration’s National Weather Service operates two tsunami warning centers: the West Coast/Alaska Tsunami Warning Center (WC/ATWC) in Palmer, Alaska, and the Pacific Tsunami Warning Center (PTWC) in Ewa Beach, Hawaii. The WC/ATWC serves as the regional Tsunami Warning Center for Alaska, British Columbia, Washington, Oregon, and California. The PTWC serves as the regional Tsunami Warning Center for Hawaii and as a national/international warning center for tsunamis that pose a Pacific-wide threat.
Some areas, such as Hawaii, have Civil Defense Sirens. Turn on your radio or television to any station when the siren is sounded and listen for emergency information and instructions. Maps of tsunami-inundation areas and evacuation routes can be found in the front of local telephone books in the Disaster Preparedness Info section.
Tsunami warnings are broadcast on local radio and television stations and on NOAA Weather Radio. NOAA Weather Radio is the prime alerting and critical information delivery system of the National Weather Service (NWS). NOAA Weather Radio broadcasts warnings, watches, forecasts, and other hazard information 24 hours a day on more than 650 stations in the 50 states, adjacent coastal waters, Puerto Rico, the U.S. Virgin Islands, and the U.S. Pacific territories.
The NWS encourages people to buy a weather radio equipped with the Specific Area Message Encoder (SAME) feature. This feature automatically alerts you when important information is issued about tsunamis or weather-related hazards for your area. Information on NOAA Weather Radio is available from your local NWS office or online.
Carry the radio with you when you go to the beach and keep fresh batteries in it.
Tsunami Generator Will Help Protect Against Future Catastrophe
A unique wave-generating machine that mimics the activity of real-life tsunamis with unprecedented realism has been used successfully in an Oxfordshire laboratory.
Tsunami Generator before being lowered into the flume. The baffles (i.e. the horizontal blue bars) stop sloshing inside the tank which gives better control of the generation of the wave. (Credit: Image courtesy of Engineering and Physical Sciences Research Council)
The simulator has copied the behavior of the first massive wave of the 2004 Boxing Day tsunami that hit Thailand.
Developed and built with Engineering and Physical Sciences Research Council (EPSRC) funding, the tsunami generator will improve understanding of how tsunamis behave.
This will aid development of more effective evacuation guidelines for parts of the world potentially at risk from future tsunamis. It will also help improve the design of buildings in susceptible areas so they are better able to withstand the impact of such events.
The innovative new facility has been developed jointly by EPICENTRE (the Earthquake and People Interaction Centre), based at University College London, (UCL) and consulting engineers HR Wallingford, at whose headquarters it is located.
Mounted in a 45 metre-long wave channel, the tsunami generator uses a pneumatic (i.e. air-driven) system comprising a fan and control valves to suck up water into a tank and then release it in a controlled way. This makes the facility fundamentally different from all other wave simulators worldwide, which generally use pistons to produce waves by pushing at the water.
The new pneumatic technique has a range of advantages over a piston-based approach. In particular, tests by UCL researchers at HR Wallingford have shown that it can reproduce the draw-down phenomenon that is characteristic of ‘trough-led’ tsunamis where the sea is sucked out first before rushing back towards the shoreline.*
Within the wave channel, or ‘flume’, the waves created by the tsunami generator are directed over a model coastal slope, enabling their behaviour and effects to be studied in detail.
Specifically, tests with this facility will be used to enhance understanding of the water flows and forces unleashed by tsunamis. This will enable buildings and infrastructure in vulnerable parts of the world to be designed and built in ways that help them withstand these destructive events.
Moreover, because this understanding will make it easier to predict the behaviour of tsunamis at shorelines and when they move inland, the tsunami generator will make it possible to strengthen emergency and contingency planning at regional, national and individual community level.
“Although the basic concept is actually quite simple, this is the only facility that has ever been able to replicate the draw-down phenomenon in the laboratory,” says Dr Tiziana Rossetto, EPICENTRE’s Director. “We’ve already used the generator to mimic the 2004 Indian Ocean tsunami at 1:75scale. The data gathered should be validated and then made available to the scientific community within the next two years.”
The tsunami generator was designed, built and tested between 2007 and 2009. EPSRC support was supplemented by additional funding from HR Wallingford and a studentship supported by consulting engineers Arup.
The aim is to make the tsunami generator available for use by other researchers from all over the world.
When an earthquake fault displaces the overlying water and causes a tsunami, waves propagate outwards from the source. Because one of the oceanic plates involved in the earthquake moves upwards and the other moves downwards, these waves are led by crests on one side of the fault and by troughs on the other. For example, in the 2004 Boxing Day tsunami in the Indian Ocean, Thailand was hit by a ‘trough-led’ wave whilst Sri Lanka was hit by a ‘crest-led’ wave.
The tsunami generator can also create longer-wavelength waves than conventional, piston-based wave generators, making the waves much more like real tsunamis. Piston-based wave generators do not have the length of stroke needed to reproduce the entire wavelength of a tsunami, even at laboratory scale. Tsunamis can have wavelengths of several hundred kilometres in the open ocean.
Tsunami waves can cause extensive loss of both life and infrastructure. Generated by earthquakes, underwater landslides, volcanic eruptions or major debris slides, tsunamis travel across seas and oceans with quite small vertical displacements, but then shoal up dramatically in coastal and nearshore depths.
The tsunami triggered by the 8.8 magnitude earthquake off the coast of Chile on 27 February 2010 led to tsunami warnings being issued across the Asia-Pacific region. In Chile itself, waves over 2.5 metres high were reported, causing a number of deaths and substantial damage to infrastructure and property. On the Chilean side, the tsunami was crest-led, whereas towards Hawaii, for instance, there was a small trough before the crest.
The 2004 Boxing Day tsunami in the Indian Ocean was triggered by an undersea earthquake off the coast of Sumatra in Indonesia. This tsunami actually consisted of three to four successive wave peaks in total. It is estimated that nearly a quarter of a million people lost their lives in the tragedy.
In populated areas, the best idea seems to be the use of seawalls in front of ports and cities. In Patong Beach in Thailand during the 2004 Indian Ocean tsunami, the seawall in front of the beach dissipated much of the energy of the tsunami and prevented the city from being destroyed. Even though the flooding because of a rise in sea level wasn’t stopped by the seawall, the force of the tsunami was, and very few casualties resulted in the area. The only areas of the city that were seriously damaged were the areas directly behind openings in the seawall designed to allow access to the beach 6. The conclusions from this report indicate that it is best to have walls offshore, with continuous protection and no holes. One design for a wall that could be implemented in ports and coastal cities is the design used in Providence, RI for the Fox Point Hurricane Barrier. This wall has three openings for ships to pass that can be closed with little warning for the protection of the harbor. Fox Point has protected the city of Providence from the floods that used to ensue destruction every time a hurricane struck, but since the barrier was built, the problem has been alleviated 21. A wall that both allows the free flow of marine traffic into and out of the port and protects the city from floods and tsunamis serves as a good balance between the necessity for protection and the need for accessibility. While the walls do not need to be taller than the tsunami to be effective, the taller a wall is, the larger the column of water stopped will be. Seawalls do not, however, completely protect a city 11 and should be used in conjunction with other methods of protection, especially trees on the coastline and dikes in rivers.
One of the most effective methods of protection from a tsunami is trees. Some villages in India, for example, had minimal casualties in the 2004 tsunami because they had planted trees along the coastline. The village of Naluvedapathy, for example, was protected by about a kilometer of trees and suffered no direct damage from the tsunami 17. Even though this would be too many trees for many areas of the coastline, a moderate thickness of trees, especially those with deep roots and dense coverage, can protect effectively against tsunamis. Mangroves, it appears, are especially good at protecting areas from tsunamis 22, so a beach with mangroves on the shore and rows of trees behind it would be well-suited to withstand a tsunami. Our plan is to plant and help sustain mangroves along empty coastlines where there is little tourism. In areas where there is tourism, the plan is to encourage the planting of low trees in a band that extends virtually uninterrupted throughout the entire shore. While these trees do not protect as effectively as mangroves, planting these would be a compromise between having accessible beaches for tourists and having protected coasts. This band of trees would have a positive effect on tourism too, for it adds to the natural beauty of the areas and provides shade. Another mechanism for preventing a tsunami from exerting its full force on the coast is to encourage the growth of coral reefs directly offshore from coasts in a way that they form an undersea wall of coral. While this is not completely effective, it has been shown to reduce the impact force of the tsunami 22. While this would only be applicable to certain parts of Peru where the water is warm enough, it would make a great method of protection for Micronesia, as well as an extra attraction for tourists.
Summary of Design Plan
Coastal Cities and Ports:
-Trees along coastline
Non-urban areas and Tourist beaches
-Development of coral reef
-Planting of extensive mangrove forests
-Trees along coastline
One of the key factors to minimizing damage caused by tsunamis is to build structures that can withstand the damage of such storms. In light of past damage assessed from tsunamis and related storms, engineers from around the world have compiled several different lists of basic requirements in a “tsunami-proof” building.
Text Box: Tsunami wave in Japan
General lessons include:
When designing our “perfect building,” we will be elevating the structure above a solid but open foundation to help alleviate the pressures from built up levels of water. Many of the buildings in the Sri Lanka tsunami had their back walls blown out due to the growing pressure from the water as it filled the buildings (Grose). Many of the building foundations also had scarring from water that funneled beneath them, accelerating from the impact. Also, in foundations of sand, whirlpools formed at building corners, which scarred and undermined the foundations even more (Minor). In addition, multi-level buildings allowed the people inside to reach heights above the wave crests to reduce casualties (Grose).
Text Box: Reinforced concrete walls in Thailand When comparing building materials, it was found that reinforced concrete structures were more likely to survive the wave forces brought by a tsunami, as compared to masonry and wood structures, which did not fare well at all (Natural Hazards). However, even brick buildings, when properly reinforced, have been found to be effective in storm situations as well. Our perfect building would be ideally made of a material, or hybrid material, that is as effective at resisting wave forces as reinforced concrete, but less costly and more readily available in areas at high risk for tsunamis.
Orientation is Key
Text Box: Harry Yeh, Civil Engineer at the Hinsdale Wave Research Lab, tests the impact of tsunami waves on these models It was found that walls that faced the ocean, allowing for a perpendicular impact from the tsunami waves, sustained a considerably higher amount of damage than walls orientated in the direction of water flow (Grose). Orientation is also important due to the massive amounts of debris that can be found in the flow resulting from tsunamis. In fact, more tsunami victims are injured or die from debris pushed along by the tsunami waves than by any other secondary cause (Dalrymple). The orientation of certain buildings with respect to the flow of coastal waters, and with respect to other buildings in the city, can minimize the debris that gets loose in a storm and has the potential to harm or kills humans (Grose).
Gone With the Wind
(Simple refugee home built from bamboo)
Research has found that once windows or doors are damaged in a building, it sets off a chain reaction that escalates the damage done to the structure. The immediate result of a failed door or window is an increase in internal pressure, which in turn causes an overall roof uplift pressure (Minor). This chain reaction continues, with the removal of the roof sheathing, wind and rain entering the building, and the progressive failure of the building frame itself. This compounded exposure greatly increases the cost of damage, and makes recovery from such natural disasters much more difficult (Minor).
So…What do we do?
Our team plans on creating the optimal, “utopian” city that lies at risk of a tsunami attack. To fulfill this dream, we must design the city and all its individual components to serve the most effective purpose against the forces of a tsunami. In the past, another MIT team came up with a protocol design for cost efficient homes designed to help the people of Sri Lanka live in tsunami-resistant homes (Brehm). I will be taking this design pattern and modeling my own after it, making any necessary changes when accounting for local materials, differences in cost, or any other necessary design changes.
The protocol design is a wood or bamboo home solidified by 4 concrete and rebar columns, each about 3meters wide. Each costing at around $1200, these 400 square feet homes would also be built on concrete or wooden blocks around 1 to 2 feet above the ground in order to allow high waters to pass under the home instead of knocking it over. In addition to this “open foundation” design, the floor plan of the house itself is also open floor, once again allowing powerful ocean waves to pass through the home and not knock it flat.