Tsunami photo album (20 photos) II. Characteristics of Tsunami Tsunami is called "Tsunami" in many western languages, and its word comes from Japanese "Tsunami", that is, "waves on the harbor" (Tianjin means "harbor"). At present, human beings can only prevent or reduce the losses caused by sudden disasters such as earthquakes, volcanoes and tsunamis through observation and prediction, but they can't stop them from happening. Tsunamis are usually caused by undersea earthquakes, with a focal point less than 50 kilometers below the seabed and a magnitude of 6.5 on the Richter scale. The wavelength of the tsunami is greater than the maximum depth of the ocean, and its spread near the seabed will not be greatly hindered. No matter how deep the ocean is, waves can pass through. The propagation speed of tsunami in the ocean is about 500 to 1000 kilometers per hour, and the distance between two adjacent waves may be as far as 500 to 650 kilometers. When the tsunami wave enters the continental shelf, the wave height suddenly increases because of its shallowness, and the wave height rolled up by this wave movement can reach tens of meters. After the tsunami triggered by the earthquake in Chile, there was chaos.
The waves caused by earthquakes are different from those on the sea. Generally, waves only fluctuate in a certain depth of water layer, while the water body fluctuation caused by earthquake is the fluctuation from the sea surface to the whole water layer on the seabed. In addition, submarine volcanic eruptions, landslides and artificial underwater nuclear explosions can also trigger tsunamis. In addition, the meteorite impact will also trigger a tsunami, and the "water wall" can reach 100 feet. Moreover, the tsunami caused by meteorites can occur in any water area, not necessarily in the earthquake zone. However, the tsunami caused by meteorites may only happen once in a thousand years. Tsunamis are very different from waves or tides generated by wind. The breeze blows across the ocean, forming relatively short waves. The corresponding flow is limited to shallow water. Strong winds can roll up waves more than 3 meters high in the vast ocean, but they can't shake the deep water. Tides [1] sweep the world twice a day. The current it produces can go deep into the seabed like a tsunami, but the tsunami is not caused by the gravity of the moon or the sun, but by an underwater earthquake, or by volcanic eruption, meteorite impact or underwater landslide. The speed of deep-sea tsunami waves can exceed 700 kilometers per hour, which can easily keep pace with Boeing 747 aircraft. Soon, but
Tsunami snapshot (14) Tsunami is not dangerous in deep water. In the open ocean, the length of a single wave below several meters can exceed 750 kilometers. The tilt of the sea surface caused by this action is very subtle, and such waves usually pass inadvertently in deep water. Tsunamis pass through the ocean quietly and unconsciously, but if they are accidentally in shallow water, they will reach catastrophic heights. Tsunami is a powerful and destructive wave. Earthquakes, volcanic eruptions, underwater collapses and landslides can all cause tsunamis. When the earthquake occurred, the seabed strata broke, and some strata suddenly rose or sank, which caused the whole water layer from the seabed to the sea surface to "shake" violently. This "jitter" is very different from the waves you usually see. Generally, waves only fluctuate near the sea surface, and the depth involved is not large, and the amplitude of waves decays rapidly with the water depth. The sea water "jitter" caused by earthquake is the fluctuation of the whole water body from the bottom to the sea surface, which contains amazing energy. The height of the wild waves caused by the tsunami can reach 10 meters to tens of meters, forming a "water wall". In addition, the tsunami has a large wavelength and can travel thousands of kilometers with little energy loss. For the above reasons, if the tsunami reaches the shore, the "water wall" will rush to the land, posing a serious threat to human life and property.
Edit the cause of the tsunami.
Earthquake/tsunami
Tsunami is a catastrophic wave, usually caused by an undersea earthquake, with a focal point less than 50 kilometers below the seabed and a magnitude of 6.5 or above on the Richter scale. Underwater or coastal landslides or volcanic eruptions may also trigger tsunamis. After an impact, the shock wave travels far away in an expanding circle on the sea surface, just like a pebble falling into a shallow pool. The tsunami wavelength is greater than the maximum depth of the ocean, and the orbital motion near the seabed is not greatly hindered. No matter how deep the ocean is, waves can pass through. Destructive waves caused by underwater earthquakes, volcanic eruptions or underwater collapses and landslides are called tsunamis. Destructive earthquakes and tsunamis only occur when there are vertical faults and the Richter scale is greater than 6.5. When the submarine earthquake causes seabed deformation, the water body near the deformation zone fluctuates greatly, resulting in tsunami.
After the tsunami (16 photos), the spread speed of the tsunami is directly proportional to the depth of its migration. In the Pacific Ocean, the speed of tsunami propagation is generally 200-300 kilometers per hour to 1000 kilometers or more. Tsunamis do not cause disasters in the deep sea, and even sailboats are hard to detect such fluctuations. When a tsunami occurs, it is safer on the high seas. Once the tsunami enters the continental shelf, the depth becomes shallow sharply and the wave height increases sharply, reaching 20 to 30 meters. This huge wave will bring a devastating disaster. Before the tsunami hit, why did the tide suddenly retreat away from the beach, and the sea rose again after a while? In most cases, the phenomenon of sea level decline occurs because the wave trough of tsunami shock wave reaches the coast first. The trough is the lowest part of the wave. If it lands first, the sea will definitely fall. At the same time, the tsunami shock wave is different from ordinary waves and has a large wavelength. Therefore, it will take quite a while for the peak to come after the trough falls. In addition, if this happens near the epicenter, it may be caused by another reason: when the earthquake occurred, the seabed ground rose and fell in a large area. At this time, the sea water near the earthquake zone also rose and fell, and then a tsunami was formed.
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Tsunamis can be divided into four types. That is, storm surge caused by meteorological change, volcanic tsunami caused by volcanic eruption, landslide tsunami caused by submarine landslide and earthquake tsunami caused by submarine earthquake. According to the materials provided by the Seismological Bureau of China, the earthquake tsunami is a strong disturbance of seawater caused by the drastic fluctuation of seabed topography when an earthquake occurs on the seabed. Its mechanism has two forms: "falling" tsunami and "rising" tsunami. "Descending" tsunami: Some tectonic earthquakes caused a large-scale sharp decline in the seabed crust. At first, the sea water rushed to the space where it suddenly sank, and there was a large area of sea water piled up on it. When the submerged seawater encounters resistance at the bottom of the sea, it turns back to the sea surface to produce compression waves, forming long waves and spreading around. The tsunami formed by this downward submarine crustal movement first appeared abnormal ebb tide along the coast. 1960 Chile earthquake and tsunami belong to this type. "Uplift" tsunami: Some tectonic earthquakes caused the submarine crust to rise sharply in a wide range, and the seawater also rose with the uplift area, and large-scale seawater accumulation appeared above the uplift area. Under the action of gravity, the seawater must maintain an equipotential surface to achieve relative balance, so the seawater diffuses from the wave source area to the surrounding areas, forming a turbulent wave. The tsunami wave formed by this uplifted submarine crustal movement first showed an abnormal climax on the coast. 1The tsunami triggered by the earthquake of magnitude 7.7 in the Sea of Japan on May 26th, 983 belongs to this type.
Edit tsunami warnings in this section.
Physical basis of tsunami early warning
How to quickly and correctly judge whether an earthquake will trigger a tsunami after a major earthquake is still an unresolved scientific problem. Nevertheless, according to the current level of understanding, we can still make some contributions to the prevention and mitigation of tsunami disasters through tsunami early warning. The physical basis of tsunami warning is that seismic waves travel faster than tsunami. P-wave earthquake, that is, the propagation speed of P-wave is about 6 ~ 7 km/s, which is 20 ~ 30 times faster than tsunami. Therefore, in terms of distance, seismic waves arrive dozens of minutes or even hours earlier than tsunamis, which depends on the epicenter distance and the propagation speed of seismic waves and tsunamis. For example, when the epicentral distance is 1000 km, the P-wave earthquake can arrive in about 2.5 minutes, while the tsunami takes about 1 hour; 1960 the tsunami triggered by the Chilean earthquake took 22 hours to reach the Japanese coast. If we can use the time difference caused by the difference between seismic wave propagation speed and tsunami propagation speed to analyze seismic wave data, quickly and accurately determine seismic parameters, and match them with the records of pre-arranged pressure gauges in the sea area where tsunami may occur (not only pressure gauges arranged on the sea surface, but also pressure gauges placed on the seabed), it is possible to judge whether the earthquake has stimulated tsunami and how big the tsunami is. Then, according to the measured bathymetric chart, seabed topographic map and the topographic features of the coastal areas where the tsunami may strike, the time and intensity of the tsunami reaching the coast are simulated and calculated, the spread process of the tsunami in this sea area is monitored by using space technologies such as satellites, remote sensing and interferometric satellite aperture radar, and the tsunami warning information is transmitted to the residents in the coastal areas where the tsunami may strike in time by using modern information technology, and the propaganda, education and education of scientific and technological knowledge on disaster prevention and mitigation are carried out in the coastal areas where the tsunami may strike. In this way, when the tsunami strikes, there is hope to save thousands of lives and avoid a lot of property losses. Tsunami early warning has a reliable physical foundation, which is not only established in theory, but also feasible in practice, and there have been successful examples. For example, 1946, the tsunami caused serious casualties and property losses in Shiloh, Hawaii. Therefore, 1948 established the Pacific Tsunami Warning Center in Hawaii, thus effectively avoiding the possible losses caused by the subsequent tsunami. If the countries along the Indian Ocean had established a tsunami warning system just like the countries along the Pacific Ocean before the Indian Ocean tsunami in 2004, the Indian Ocean tsunami triggered by the Sumatra-Andaman earthquake would never have caused such huge casualties and property losses. The tsunami warning mentioned above is more effective for "marine tsunami". For "offshore tsunami" (also called "local tsunami"), that is, the submarine earthquake that caused the tsunami is very close to the coast, for example, a tsunami with only a few tens to several hundred kilometers, because the propagation speed of seismic wave is different from that of tsunami, the time difference is only a few minutes to several tens of minutes, so the tsunami early warning is more difficult to be effective. In order to quickly and correctly judge whether the earthquake triggered a tsunami after a major earthquake, reduce the misjudgment and false alarm, especially the early warning of "offshore tsunami", and improve the early warning level of tsunami, it is necessary to strengthen the research on tsunami physics. (Excerpted from: Popular Science News 2006 65438+1October 24th)
Roaring waves
According to the theory of modern plate structure, Chile is a subduction zone where the Pacific plate collides with the South American plate, and it is located in the volcanic activity zone around the Pacific Ocean. This special geological structure leads to the extremely unstable surface of Chile. Since ancient times, volcanoes have been erupting, earthquakes have been repeated, tsunamis have appeared frequently, and disasters have often come. 2 1 In the early morning of May 26th, a strong earthquake, which is rare in the world earthquake history, suddenly occurred on the seabed near puerto montt, Chile. Large and small earthquakes lasted until June 23rd, and there were 225 earthquakes of different magnitudes in 1 several months. There are more than a dozen earthquakes of magnitude 7 and above, and 3 earthquakes of magnitude 8 and above.
Tsunami early warning system
Earthquakes can trigger tsunamis, so the early warning information of tsunamis should be provided by the earthquake monitoring system. In earthquake-prone areas around the world, such as the Pacific coast and the Indian Ocean coast, there should be a perfect earthquake monitoring network.
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[2] Soon after the violent vibration, the huge waves roared, crossed the coastline and fields, and quickly attacked the cities and villages on the shore, and people disappeared into the huge waves in an instant. All the facilities and collapsed buildings in the port were swept away by the rough waves. Afterwards, the beach was a mess, full of broken wood and human and animal bodies. The disasters brought by earthquakes and tsunamis to human beings are enormous. At present, human beings can only prevent or reduce the losses caused by sudden disasters such as earthquakes, volcanoes and tsunamis through prediction and observation, but they cannot control their occurrence. Yu Fujiang, deputy director of the Marine Environment Forecasting Office of the Marine Environment Forecasting Center of the State Oceanic Administration, said that China is located on the west coast of the Pacific Ocean, with a continental coastline of 1.8 million kilometers. However, because the coast of Chinese mainland is blocked by Ryukyu Islands and Southeast Asian countries, the continental shelf is wide. After the transoceanic tsunami enters this sea area, the energy decays rapidly, which has little impact on the mainland coast. Because seismic waves travel along the crust much faster than seismic tsunami waves, tsunamis can be predicted in advance. However, tsunami prediction is more difficult than earthquake detection. Because the seabed topography is too complex, it is difficult to accurately measure the deformation of the seabed. 65438-0964 A global tsunami early warning system coordination group was established internationally. Due to the frequent occurrence of tsunamis in the Pacific Ocean, the tsunami early warning system is very developed. After the earthquake 15 minutes, the Pacific Tsunami Warning Center issued early warning information from Honolulu Branch to 26 countries participating in the joint early warning system. If there is an early warning system in the Indian Ocean, perhaps people can make better use of the precious time from the earthquake to the tsunami landing on the Indian Ocean coast.
Edit the five deadly tsunamis in this history.
V. Number of tsunami deaths caused by volcanic eruption in Indonesia: 36,000 Cause: Volcano eruption1.883 In August, Krakato volcano in Indonesia erupted, which was the worst in human history. This volcanic eruption can be heard as far away as Australia. The tsunami wave caused by volcanic eruption is as high as 130 feet (40 meters). According to the US Geological Survey (USGS), only Java and Sumatra responded to the tsunami in the South China Sea of China.
In La Island, the waves washed away 165 villages. The waves triggered by the tsunami did not stop until 4,350 miles (7,000 kilometers) away in the Arabian Peninsula. Fourth place, 1782, South China Tsunami 1782, South China Tsunami Death Number: More than 40,000 Reasons: The historical record of this disaster is incomplete, but a Russian tsunami catalogue published in 1964 thinks that 1782 (that is, forty-seven years of Qianlong) (caused by the Lisbon earthquake in Portugal)
It is reported that the death toll from the tsunami in Taiwan Province Province exceeded 40,000, and the land on the island was flooded for more than 75 miles (120km). Third place, tsunami caused by Lisbon earthquake in Portugal. The number of tsunami deaths caused by Lisbon earthquake in Portugal: 60,000. Reason: submarine earthquake1755165438+10, and the Atlantic earthquake shook southwest Portugal. Lisbon went bankrupt because of the earthquake and the fire that followed. At the same time, the tsunami triggered by the volcanic eruption in Crete, ancient Greece
At that time, the tsunami triggered by the earthquake swept the coastal towns of Portugal, Spain and Morocco. It is estimated that the waves that hit Lisbon are as high as 18 feet (6 meters). The second is the tsunami caused by the volcanic eruption in Crete, ancient Greece. The number of tsunami deaths caused by volcanic eruption in Crete, ancient Greece: more than 654.38+ 10,000. Reason: The volcanic eruption occurred around 1500 BC, and the submarine volcanic eruption on the Mediterranean island of Scylla (now also called santorini Island) produced great destructive power. Tsunami triggered by the eruption of Crete volcano in ancient Greece
According to the research of the National Oceanic and Atmospheric Administration (NOAA) Tsunami Research Center, this volcanic eruption created the first tsunami in history. The exact death toll will never be known, but geographical evidence shows that the tsunami flooded 50 feet (15 meters) off the coast of Crete. First, the number of people killed by the Indian Ocean tsunami in 2004: about 226,000. Cause: Haiti earthquake. On February 26th, 2004, an earthquake measuring 9. 1-9.3 on the Richter scale occurred off the coast of Sumatra Island, Indonesia, with a duration of 10 minute. The earthquake triggered the Indian Ocean tsunami in 2004.
The tsunami even endangered the coastal residents of Somalia. Indonesia alone killed1660,000 people, and Sri Lanka killed 35,000 people. In India, Indonesia, Sri Lanka, Myanmar, Thailand, Maldives and East Africa, more than 2 million people are homeless. There were 226,000 deaths, ranking only the fourth among the earthquake deaths, but the first among the tsunami deaths.
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Scholars in China found that there were tsunami records in Laizhou Bay and Huangxian County in China in 47 BC (that is, in the early years of the Western Han Dynasty) and in 173 AD (Xiping Year of the Eastern Han Dynasty). These records are widely quoted by foreign scholars and are considered as the earliest two tsunami records in the world. The tsunami area in the world is roughly consistent with the earthquake zone. There are about 260 recorded destructive tsunamis in the world, averaging about once every six or seven years. Earthquakes and tsunamis around the Pacific Ocean account for about 80%. The earthquakes in the Japanese archipelago and its adjacent waters account for about 60% of the Pacific earthquakes and tsunamis, and Japan is the country suffering from the most severe earthquakes and tsunamis in the world. Recently, it triggered a large-scale tsunami. According to the report of Reuters, a strong earthquake of 1 1 1 occurred in the northeast coast of Japan at 14: 46 pm (Beijing time 13:46), which was estimated to reach 8.8 on the Richter scale, and then occurred again at 65446 on March. Witnesses in the earthquake zone said that this may be the earthquake with the highest magnitude in Japan for more than 20 years. In addition, witnesses said that the earthquake caused many buildings in Tokyo to shake and caused "many injuries." At least one building caught fire and triggered a tsunami 10 meters high. Beijing, 2010/0126 October According to foreign reports on the 26th, an earthquake occurred in Sumatra, Indonesia a few days ago and caused a tsunami. So far, at least 40 people have died and more than 380 people are missing. According to CNN, Indonesia's national disaster management department said that a strong earthquake of magnitude 7 or above occurred in Sumatra on the 25th local time, which triggered a tsunami, and Mentawai islands on the west coast of Sumatra was hit by the tsunami. Officials said that by the afternoon of 26th local time, 40 people had died in mentawai islands and other places due to the earthquake and tsunami. The bodies of some villagers were washed up on the coast and found. Earlier reports said that the tsunami killed 23 people. It is also reported that there are currently more than 380 people missing in Indonesia. At present, only about 40 of the more than 200 villagers in Betumunga village along the coast of South Paget Island in mentawai islands have been rescued, and at least 167 people are missing. Most of the missing persons are women and children. It is believed that another 65,438,000 people were passengers on ships lost contact due to the tsunami. In Nanbagai Island, the huge waves caused by the tsunami invaded the coastal villages within 600 meters; The waves in North Bagai Island directly hit the roof of the house. The big waves also prevented rescuers from rushing to the disaster area in time. BEIJING 10/26 According to the latest news from AFP, Indonesian officials said that the death toll caused by the tsunami caused by the earthquake in Indonesia has risen to 108, and hundreds of people are missing. Earlier, it was reported that Indonesia's national disaster management department said that a strong earthquake of magnitude 7 or above occurred in Sumatra on the 25th local time, which triggered a tsunami. 10 villages in the Indonesian archipelago were hit by the tsunami. On South Paget Island in mentawai islands, west of Sumatra Island, the huge waves caused by the tsunami invaded coastal villages within 600 meters; The waves in North Bagai Island directly hit the roof of the house. The big waves also prevented rescuers from rushing to the disaster area in time. On June 26th, 2004, 65438+February 26th, 2004, a submarine earthquake of magnitude 9 occurred in the waters near Sumatra Island, Indonesia. The tsunami hit Sri Lanka, India, Thailand, Indonesia, Malaysia, Bangladesh, Maldives, Myanmar and the east coast of Africa, killing more than 300,000 people. The exact number of deaths has been impossible to count. See the 2004 Indian Ocean Earthquake. 1In July 1998, two submarine earthquakes of magnitude 7.0 occurred in Papua New Guinea, causing about 2 100 deaths. 1992 A tsunami occurred in Nicaragua in September. 1On August 25th, 883, dutch east indies volcano erupted, which triggered a tsunami and killed 36,000 people. Pay attention to the location and date of the typhoon source, the number of deaths in the affected areas due to wave height (m), vancouver island1700 65438+1October 26th? Northern California to vancouver island and Japan? Portugal175511October 16 Western Europe, Morocco and the West Indies 60000 Ryukyu Islands1771Ryukyu Islands/Kloc-0 on April 24th, 85. Kloc-0/883 August 26th 35 Java and Sumatra 36000 Celebes Sea 1976 August 16 30 Philippine Islands 5000 Sumatra Northwest Coast 2004 12.26? More than 300,000 tsunamis in the Indian Ocean: the biggest tsunami in more than a hundred years: ▲ 1883, Krakato volcano in Indonesia erupted, which triggered a tsunami, affecting Sumatra and Java in Indonesia, killing 36,000 people. ▲ 1896, an earthquake of magnitude 7.6 occurred in Japan, and the tsunami caused by the earthquake killed more than 20,000 people. ▲ 1906, an earthquake occurred in the waters near Colombia, and the tsunami affected some cities in Colombia and Ecuador. ▲ 1960, a 9.5-magnitude earthquake (the strongest earthquake in history) occurred at the bottom of the Pacific Ocean near south-central Chile, triggering the largest tsunami in history, affecting countries along the Pacific Ocean, killing tens of thousands of people, even hundreds of people in Japan and Russia far west of the Pacific Ocean. ▲ From 1992 to 1993, three tsunamis occurred in the Pacific Ocean, killing more than 2,500 people. ▲ On 2011March 1 10, a 9.0-magnitude earthquake occurred in Japan, which triggered a huge tsunami and affected Pacific Rim countries. (Japan officially revised it to a 9.0 earthquake)
Edit this paragraph tsunami self-help
What should people do when they encounter a tsunami while traveling? Life-saving tip: Don't rush back to your nest after hearing the tsunami warning. How to escape from the tsunami 1 An earthquake is the most obvious precursor of a tsunami. If you feel a strong vibration, don't go near the mouth of the sea and rivers. If you hear the report of an earthquake nearby, you should be prepared to prevent the tsunami and pay attention to TV and radio news. Remember, tsunamis sometimes reach thousands of kilometers away from the source a few hours after an earthquake. Second, ships at sea should avoid returning to the port after hearing the tsunami warning. The gap and turbulence caused by the tsunami in the harbor are very dangerous. If there is enough time, the shipowner should take the boat out to sea before the tsunami comes. If there is no time to sail out of the harbor, everyone should evacuate the ships moored in the harbor. 3. When the tsunami lands, the seawater often rises or falls obviously. If you see the sea surface retreating at an unusually fast speed, you should immediately evacuate to a higher place inland. Everyone should have a first aid kit, which should contain enough medicine, drinking water and other necessities for 72 hours. This applies to tsunamis, earthquakes and all sudden disasters.