What is a Supertsunami?

A tsunami is a destructive wave caused by a submarine earthquake, volcanic eruption, submarine landslide, or meteorological change. The tsunami has a wave speed of 700 to 800 kilometers per hour and can cross the ocean in a few hours; the wavelength can reach hundreds of kilometers and can It travels thousands of kilometers with very little energy loss. In the vast ocean, the wave height is less than one meter, but when it reaches shallow coastal waters, the wavelength decreases and the wave height increases sharply, reaching tens of meters, forming a "water wall" containing huge energy. ". The tsunami is mainly controlled by the bottom terrain, the geometry of the coastline, and the characteristics of the waves. The whizzing waves and ice walls repeat every few minutes or tens of minutes, destroying the embankment, flooding the land, and robbing life and property, which is extremely destructive. The global tsunami occurrence area is roughly consistent with the earthquake zone. About 260 destructive tsunamis have been recorded worldwide, with an average of about six or seven years. About 80% of the earthquake and tsunami occurred in the Pacific Rim. The earthquakes in the Japanese islands and the surrounding seas accounted for about 60% of the Pacific earthquake and tsunami. Japan is the country that suffered the most from the earthquake and tsunami in the world.

A tsunami is a destructive wave caused by a submarine earthquake, volcanic eruption, submarine landslide, or meteorological change. The tsunami has a wave speed of 700 to 800 kilometers per hour and can cross the ocean in a few hours; the wavelength can reach hundreds of kilometers and can It travels thousands of kilometers with little energy loss; in the vast ocean, the wave height is less than one meter, but when it reaches the shallow coastal waters, the wavelength decreases and the wave height increases sharply, reaching tens of meters, forming a "water wall" containing huge energy. ". The tsunami is mainly controlled by the bottom terrain, the geometry of the coastline, and the characteristics of the waves. The whizzing waves and ice walls repeat every few minutes or tens of minutes, destroying the embankment, flooding the land, and robbing life and property. The global tsunami occurrence area is roughly consistent with the earthquake zone. About 260 destructive tsunamis have been recorded around the world, with an average of about six or seven years. About 80% of the earthquake and tsunami occurred in the Pacific Rim. The earthquakes in the Japanese islands and the surrounding seas accounted for about 60% of the Pacific earthquake and tsunami. Japan is the country that suffered the most from the earthquake and tsunami in the world.

Chinese name: Tsunami

Foreign name: seaquake

Tsunami formation

Tsunami generation principle (English) ^[1] A tsunami is a catastrophic wave, usually caused by a submarine earthquake with a source within 50 kilometers below the ocean floor and a magnitude greater than 6.5 on the Richter scale. Tsunami can also be caused by underwater or coastal landslides or volcanic eruptions. After a shock, the oscillating wave spreads over a large distance on the surface of the sea, like a wave generated by a pebble falling into a shallow pond. The wavelength of the tsunami is greater than the maximum depth of the ocean, and the orbital motion is not much hindered near the bottom of the ocean. Waves can propagate past regardless of the depth of the ocean.

Tsunami classification

Tsunami (12 photos)

Tsunami can be divided into three categories according to its cause: earthquake tsunami, volcano tsunami, and landslide tsunami. Earthquake tsunami is the strong disturbance of the seawater caused by the rapid fluctuation of the terrain on the sea floor when an earthquake occurs on the sea floor. The mechanism has two forms: a "falling" tsunami and a "bulging" tsunami.

"Descent" tsunami: Certain tectonic earthquakes caused a large-scale drastic decline of the submarine crust. The seawater first poured into the space where the subsidence suddenly subsided, and a large-scale accumulation of seawater appeared above it. After resistance, the compression wave is turned back to the sea to form a long wave, which spreads and spreads to the surrounding area. The tsunami formed by this descending submarine crustal movement first appears as an abnormal ebb on the coast. The Chilean tsunami of 1960 belongs to this type.

"Uplift" tsunami: Some tectonic earthquakes caused a large-scale sharp rise in the submarine crust, and the seawater also rose along with the uplift zone, and a large-scale accumulation of seawater appeared above the uplift zone. Under the action of gravity, the seawater must maintain a constant The potential surface is relatively balanced, so the seawater spreads from the wave source area to the surrounding area, forming a turbulent wave. The tsunami wave formed by this uplift-type submarine crustal movement first appeared as an abnormal high tide phenomenon on the coast. On May 26, 1983, the tsunami caused by the magnitude 7.7 earthquake in the Central Japan Sea was of this type.

Relative to the disaster site, the tsunami can be divided into two types: remote tsunami and local tsunami.

Distant tsunami: Distant tsunami refers to a tsunami that crosses the ocean or spreads from a great distance. It is also called a transoceanic tsunami. Tsunami waves are long ocean waves. Once generated at the source, they can travel thousands of kilometers with little energy attenuation without blocking by island groups or large shoals or shallow water shelves. Therefore, they may cause thousands of kilometers away. Suffering from a tsunami disaster. For example, the tsunami that hit Indonesia at the end of 2004 affected Sri Lanka thousands of kilometers away. In 1960, the Chile tsunami also caused severe disasters to Hawaii and Japan thousands of kilometers away.

Local tsunami: Most of the tsunami are local tsunami or local tsunami. Because the local tsunami is relatively close from the source of the earthquake and tsunami to the affected coastal area, the time it takes for the tsunami wave to reach the coast is also short, only a few minutes, and dozens more. In this case, the tsunami warning time is shorter or there is no warning time at all, which often causes extremely severe disasters.

Tsunami distribution

The world's tsunami-prone areas are the Hawaiian Islands, Alaska Region, Kamchatka-Thousand Islands, Japan and surrounding areas, China and its neighboring areas, the Philippines Islands, Indonesia areas, New Guinea areas-Solomon Islands, New Zealand-Australia and the South Pacific, Colombia-northern Ecuador and the coast of Chile, Central America and the United States, the western coast of Canada, and the northeastern coast of the Mediterranean.

Tsunami hazard

Scene after the tsunami (13 photos)

When the tsunami struck, the oscillating waves spread in an ever-increasing circle on the surface of the sea and reached far away. At a high speed of 600-1000 kilometers per hour, it employs 10,000 to 20,000 kilometers on an unobstructed ocean surface, setting off a shore wave of 10-40 meters high, engulfing everything that is affected, sometimes the most The tsunami on the coast that arrived first may be a trough of valleys, where the water level drops, exposing the bottom of the shoal; a few minutes later, the crests come and they retreat and advance, causing devastating damage. ^[2]

Soon after the violent shaking, the huge waves roared, smashing across the coastline and across the fields in a destructive and violent manner, slamming the cities and villages on the shore, and people disappeared into the huge waves. All the facilities of the port, the collapsed buildings, were swept up by the robbery. After the incident, the beach was a mess, full of broken wood and human and animal corpses. ^[2]

Tsunami protection

Tsunami Warning

Physical basis: The physical basis of the tsunami warning is that the propagation speed of the seismic wave is faster than that of the tsunami. Seismic longitudinal waves, or P waves, travel at a speed of about 6 to 7 km / s, which is 20 to 30 times faster than a tsunami. Therefore, in the distance, seismic waves reach tens of minutes or even hours earlier than the tsunami. The specific value It depends on the epicenter distance and the propagation speed of the seismic wave and tsunami. For example, when the epicenter distance is 1000 kilometers, the longitudinal wave of the earthquake can reach in about 2.5 minutes, and the tsunami takes about an hour; the tsunami caused by the Chilean earthquake in 1960 reached the coast of Japan 22 hours later. ^[3]

If you can use the time difference caused by the difference between the propagation speed of the seismic wave and the tsunami to analyze the seismic wave data, quickly and accurately determine the seismic parameters, and the pressure gauge installed in advance in the sea area where tsunami may be generated (not only should it be installed on the sea surface The pressure gauge above should be matched with the record of the pressure gauge installed on the sea floor, and it is possible to make a judgment as to whether the earthquake triggered the tsunami and the scale of the tsunami. Then, based on the measured water depth maps, seabed topographic maps, and topographic features of coastal areas that may be hit by the tsunami, the time and intensity of the tsunami reaching the coast are simulated and calculated, and space technologies such as satellite, remote sensing, and interferometric satellite aperture radar are used to monitor The process of tsunami spreading in the sea area, using modern information technology to timely transmit tsunami warning information to residents of coastal areas that may be hit by the tsunami, and carry out scientific and technological knowledge on preventing and mitigating tsunami disasters in the coastal areas that may be hit by the tsunami. Advocacy, education, outreach and training and exercises in response to the tsunami disaster. In this way, there is hope to save tens of thousands of lives and avoid large property losses when the tsunami strikes. ^[3]

The tsunami warning has a reliable physical foundation. It is not only theoretically valid, but also practical, and has already been successfully used. For example, in 1946, the tsunami caused serious casualties and property damage to Hawaii's "Hilo" city. As a result, the Pacific Tsunami Warning Center was established in Hawaii in 1948, which effectively avoided the possible losses caused by the tsunami in the future. If the countries along the Indian Ocean can establish a tsunami warning system like the countries along the Pacific Ocean before the 2004 Indian Ocean tsunami, then the Indian Ocean tsunami caused by the Sumatra-Andaman earthquake will not cause such huge casualties and property. loss. ^[3]

The tsunami warning described above is more effective for "ocean tsunami". However, for the "offshore tsunami" (also known as "local tsunami"), that is, the tsunami that triggered the tsunami is very close to the coast, for example, a tsunami with only tens to hundreds of kilometers, due to the difference between the propagation speed of the seismic wave and the tsunami The time difference is only a few minutes to tens of minutes, and early tsunami warning is more difficult to take effect. ^[3]

Early warning system: Earthquakes can trigger tsunami, so the tsunami warning information 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 complete earthquake monitoring network.

Tsunami tsunami escape

1. The earliest signal of an earthquake and tsunami is a strong ground vibration. There is a time difference between the arrival of the seismic wave and the tsunami, which is good for people's prevention. If you feel a strong vibration, don't go near the sea or the river's entrance. If you hear reports of nearby earthquakes, be prepared for tsunami protection and watch TV and radio news. Keep in mind that tsunami sometimes reaches thousands of kilometers away from the source of the earthquake just hours after the earthquake.

2. If it is found that the tide suddenly fluctuates abnormally, the sea level drops significantly, or a huge wave hits, it should be evacuated from the shore at the fastest speed.

3. When the water recedes abnormally before the tsunami, many marine animals such as fish and shrimp are often left in the shallows, and the scene is spectacular. At this time, do not go to pick up fish or watch the excitement. You should leave the coast quickly and move to the inland high places.

4. In the event of a tsunami, ships sailing on the sea cannot return to the port or dock, and should immediately sail to the deep sea area, which is safer than the coast.

5. Everyone should have a first aid kit, which should contain enough medicines, drinking water and other necessities for 72 hours. This applies to tsunamis, earthquakes and all sudden disasters.

Tsunami self-help and mutual rescue

1. If you unfortunately fall into the water during a tsunami, try to catch floating objects such as wooden boards and avoid collision with other hard objects.

2. Do not raise your hands or struggle in the water. Minimize your movements. You can float on the water and follow the waves. This can not only avoid sinking, but also reduce the unnecessary consumption of physical energy.

3. If the seawater temperature is low, do not take off your clothes.

4. Try not to swim, to prevent the body heat from being dissipated too quickly.

5. Don't drink sea water. Not only can seawater not quench thirst, but it can cause hallucinations, leading to mental disorders and even death.

6. Move closer to other people who fall into the water as much as possible, not only to help and encourage each other, but also because it is easier for rescuers to find out because of the expansion of the target.

7. If people immerse in seawater for a long time, the heat loss will cause the body temperature to drop. After being rescued ashore, it is best to put the drowning person in warm water to restore their body temperature. If there is no condition, they should try to put on quilts, blankets, coats and other insulation as much as possible. Be careful not to use local warming or massage methods, let alone drowning people. Drinking alcohol can only dissipate heat faster. It is good to drink some sugar water for those who fall into the water. It can supplement the body's water and energy.

8. If the person falling into the water is injured, first-aid measures such as hemostasis, bandaging, and fixation shall be taken, and the seriously injured person shall be sent to the hospital for treatment in time.

9. Remember to remove inhaled substances in the nasal cavity, mouth and abdomen of the person in time. The specific method is: put the tummy's belly on your thigh, press from the back, and pour out the inhaled materials such as seawater. If the heartbeat or breathing stops, you should immediately alternate between mouth-to-mouth resuscitation and cardiac compression. ^[4]

Tsunami

In the 16th century BC , a violent eruption occurred on the Santorini volcano north of Crete. After the volcanic eruption, only Thira and some small islands stood in the Aegean Sea. Tsunami experts later discovered that the tsunami waves caused by the volcanic eruption were more than 90 meters above sea level and reached the Nile River valley 300 kilometers away.
On September 20, 1498 , a tsunami caused by a magnitude 8.6 earthquake on the bottom of Tokaido, Japan. The maximum wave height of the tsunami was 15-20 meters. More than 1,000 buildings were destroyed in Ise Bay, and more than 5,000 people were drowned. Many, Ise-Shima was severely affected. According to the "Taimingshi" of Shizuoka Prefecture, 26,000 people were killed; 10,000 people were drowned in Mie Prefecture.
The Pacific coast is vulnerable to catastrophic tsunamis. Japan has suffered more than 20 tsunami attacks since 1596. In 1703, the tsunami struck Kurizu, Japan, killing 100,000 people. In 1933, the east coast of Honshu Island in Japan was hit by a tsunami, and about 3,000 people died.
On November 1, 1755, shortly after the strong earthquake in the waters near Lisbon, the coast water level receded, revealing the entire bottom of the bay, and curious people went down to the bottom of the bay to "explore." However, within a few minutes, the crest came, the huge waves rushed to the coast, swept away tens of thousands of residents, and the city was flooded. The "explorators" on the bottom of the sea naturally became the first victims of the tsunami. . The Atlantic Ocean's harbour, Cadiz, was also hit by a 10-meter wave. The tsunami also swept the Netherlands, Britain and Madeira, Azores, Lesser Antilles and other places.
On February 5, 1783, a quake struck the Strait of Messina, which was accompanied by a tsunami and floods, which brought the city of Messina to extinction. On April 8, the same year, the earthquake struck again. After two months of torture, more than 30,000 people died directly from the earthquake and tsunami. On December 28, 1908, a 7.5-magnitude earthquake struck the Strait of Messina and caused a tsunami, killing 85,000 people in Messina.
On August 26 and 27, 1883 , the Krakatau volcano erupted, spraying 20 cubic kilometers of magma into the Sunda Strait between Sumatra and Java. When the volcanic eruption reached its highest tide, the magma vent collapsed and triggered a tsunami ... The waves in Java Merak were as high as over 40 meters, and the giant waves in Sumatra's Betong caves were as high as 36 meters. 36 thousand people were killed. The tsunami spread across the world, and even the tidal viewfinder of the English Channel recorded its shock waves.
In 1896 (Meiji 29), the Japan Sanriku tsunami had a magnitude of 7.6 on the Richter scale and no direct earthquake disaster, but more than 27,000 people died in the tsunami. The tsunami caused by the famous Japanese Great Kanto Earthquake was also alarming, causing more than 8,000 ships to sink, drowning more than 50,000 people, and paralyzing large and small ports along the coast.
On April 1, 1946, there was also a tsunami in Hawaii. The tsunami was caused by a magnitude 7.3 earthquake that struck the seafloor near the Aleutian Islands, 3,750 kilometers from Hawaii. Forty-five minutes after the quake, the huge waves first hit Unimark Island in the Aleutian Islands, completely destroying a reinforced concrete lighthouse on a 12-meter-high rock and a radio on a 32-meter-high platform. Differential tower. The tsunami swept southward at a jet-like speed, destroying 488 buildings on the island of Hawaii and killing 159 people.
In May 1960, a strong earthquake struck the south-central Chilean sea floor, triggering a huge tsunami, causing tens of thousands of deaths and disappearances, all the docks along the coast were paralyzed, and 2 million people were left homeless. This is the area of influence in the world The largest and most severe tsunami disaster.
On July 17, 1978, a strong earthquake measuring 7.1 on the Richter scale struck the Bismarck Sea, 12 kilometers northwest of Papua New Guinea, in the western Pacific. A magnitude 5.3 aftershock occurred 20 minutes later. Everything seemed to return to calm after that, and nearly 10,000 villagers living in the narrow strip between the northwest coast of Papua New Guinea and the Sisano lagoon, did not know that a greater disaster was imminent. A strange rumbling sound from far to near, many villagers thought that it was just a jet plane coming out, one after another came out to watch the lively, in a blink of an eye, a giant wave of 20 kilometers long and 10 meters high whistled sweeping After that, 7 villages that stretched across the Sisano lagoon and the beach were suddenly submerged in the waves. In just a few minutes, this scenic resort in the Western Pacific has turned into a hell on earth. Only 2527 of 10,000 people survived, more than 7,000 people died or disappeared, and more than 70% of the survivors were adults, and children rarely survived.
From September 1992 to July 1993, the tsunami struck Nicaragua on the Pacific coast, the Indonesian islands, and Okushiri Island in Japan three times. The tsunami claimed a total of 2,500 lives. ^[5]
The Indian Ocean Tsunami on December 26, 2004 This tsunami was second only to the tsunami caused by the 9.5 earthquake in Chile in 1960, becoming the second strongest earthquake and tsunami in history. Statistics as of January 10, 2005 show that the Indian Ocean earthquake and tsunami has killed 156,000 people, which may be the world s worst tsunami disaster in nearly 200 years.
On March 11, 2011, a magnitude 9.0 earthquake struck Japan, which caused a huge tsunami and killed nearly 30,000 people. Pacific Rim countries are affected.
The earthquake and tsunami in Indonesia on September 28, 2018, as of September 29, have killed at least 384 people there. (See the main entry for details: 9/28 Indonesia earthquake). ^[6]
On September 28, 2018, Sulawesi, Indonesia was pinched by a strong earthquake and tsunami, and many cities along the coast were severely damaged. The number of victims has increased to 1,200. ^[7]

Tsunami History

Chinese scholars have discovered that in 47 BC (the first year of the Western Han Dynasty) and 173 AD (the second year of the Eastern Han Dynasty), China recorded the tsunami in Laizhou Bay and Huangxian County in Shandong. These records have been widely cited by foreign scholars and are considered to be the earliest two tsunami records in the world. About 500 years later, tsunami records of 2 to 3 meters in the magnitude 8.4 earthquake on the bottom of the sea south of the Shikoku region were recorded.

Tsunami event

Fifth place, tsunami caused by volcanic eruption in Indonesia

Death toll: 36,000

Cause: Volcanic eruption

In August 1883, the volcanic eruption in the volcanic island of Krakatau, Indonesia, was the worst in human history. The volcanic eruption can be heard as far away as Australia. The tsunami waves caused by the volcanic eruption were as high as 130 feet (40 meters). According to the United States Geological Survey (USGS), the waves washed away 165 villages in Java and Sumatra alone. The waves from the tsunami did not cease until 4,350 miles (7,000 kilometers) away on the Arabian Peninsula.

Fourth place, 1782, South China Tsunami

In 1782, the South China Tsunami

Death toll: more than 40,000

Cause: Earthquake

The historical record of the disaster is not complete, but a Russian tsunami catalogue published in 1964 considers 1782 (the 47th year of Qianlong) (Translator's Note: "History of the Qing Dynasty, Shi XV, Disaster Disaster" is not recorded The death toll from the tsunami in Taiwan was more than 40,000, and the land on the island flooded more than 75 miles (120 kilometers).

Third place, tsunami caused by the earthquake in Lisbon, Portugal

Number of deaths: 60,000

Cause: Submarine earthquake

In November 1755, a major earthquake in the Atlantic shook southwestern Portugal. The city of Lisbon went bankrupt due to the earthquake and subsequent fires. At the same time, the tsunami triggered by the earthquake swept coastal towns of Portugal, Spain and Morocco. The waves hitting Lisbon were estimated to be 18 feet (6 meters) high.

Second place, the tsunami caused by the volcanic eruption of Crete in ancient Greece

Death toll: 100,000 or more

Cause: Volcanic eruption

Around 1500 BC, the volcanic eruption on the seabed of Thira (also known as Santorini) in the Mediterranean Sea was extremely destructive. According to the National Oceanic and Atmospheric Administration (NOAA) Tsunami Research Center, the volcanic eruption created the first tsunami in history. The exact number of deaths will never be known, but geographical evidence suggests that the tsunami flooded 50 feet (15 meters) of the coast of Crete.

First place, Indian Ocean Tsunami 2004

Number of deaths: about 226,000

Cause: Haiti earthquake

On December 26, 2004, a magnitude 9.1-9.3 earthquake struck the coast of Sumatra, Indonesia, which lasted up to 10 minutes. The tsunami triggered by the earthquake even endangered residents of the coast as far away as Somalia. Indonesia alone killed 166,000 people and Sri Lanka killed 35,000 people. More than 2 million people are homeless in India, Indonesia, Sri Lanka, Myanmar, Thailand, Maldives and East Africa.

The number of deaths was 226,000, which ranked only the fourth among the death tolls from the earthquake, but ranked first among the tsunami deaths. ^[8]