What is an earthquake? What are the depth focuses of earthquakes?

The Earth is our home and the most suitable planet for human habitation in the known universe. However, while the earth has given us peace and tranquility, a series of disasters have never stopped. Among them, earthquakes are the most subversive. Wherever it went, houses collapsed, and when everything returned to calm, the entire town was beyond recognition. Let us turn back the time and review the shocking earthquakes that occurred on the earth with a critical eye!

1. Earthquakes - the number one disaster

The suddenness, destructiveness and unpredictability of earthquake disasters have brought serious harm to social and economic development, human life safety and social stability. . About 5 million earthquakes occur around the world every year, with an average of more than 10,000 earthquakes every day, but most of them are not easily noticed by people. In history, various natural disasters have destroyed 52 cities around the world, 27 of which were destroyed by earthquakes. Earthquakes are truly the "number one disaster".

Tips

Earthquake disasters that have killed tens of thousands of people in the world in the past thousand years

(This table is based on data from the Earth Science Dictionary, China Earthquake Information Network and Comprehensive compilation of data from the U.S. Geological Survey website)

(Note: Foreign seismic data are based on the U.S. Geological Survey data, and domestic seismic data are based on the China Earthquake Information Network, the same below)

(*Unless otherwise specified, all below indicate Richter scale)

my country’s earthquake disasters are also among the highest in the world. Due to the high frequency, high intensity, wide range, shallow epicenter, and dense population of earthquakes in our country, the seismic resistance of buildings is generally low. Earthquakes bring us huge casualties. Since the 20th century, 1.7 million people have died from earthquakes around the world, of which 630,000 were in my country, accounting for 37% of the total earthquake deaths.

2. The world's largest earthquake

The largest earthquake was the 9.5-magnitude earthquake that occurred in Chile in 1960. The tsunami caused by this earthquake turned 50% of the buildings in a Chilean city into rubble fields. More than 100 breakwaters along the coast were washed away, more than 2,000 ships were destroyed, and the loss was US$550 million. All houses and industrial buildings in the epicenter area were destroyed. About 130,000 square kilometers of land subsided by 2 meters.

This huge earthquake caused several lakes to disappear, two hills to disappear, many places were flattened, and six volcanoes erupted again. At the same time, the earthquake triggered a tsunami. The huge waves swept across the Pacific Ocean at a speed of 600 kilometers per hour, causing a land mass of about 500,000 square kilometers on the seabed to rise by nearly 10 meters. The area reached as far away as Hawaii, Japan, eastern New Zealand, southeastern Australia and as far away as Alaska and the Aleutian Islands.

Tips

The earthquake with the largest number of fatalities

On January 23, 1556, the 34th year of Jiajing reign in the Ming Dynasty, an 8.0 magnitude earthquake occurred. Occurred in Huaxian County, Shaanxi Province. The earthquake killed 830,000 people, making it the deadliest earthquake in the world. Such a high mortality rate is related to many factors. The earthquake zone is located in river valley basins and alluvial plains, with thick loose sediments. The liquefaction of sand during the earthquake increased the damage to buildings; the collapse of cave dwellings also caused huge casualties; the earthquake occurred at midnight, and people were sleeping soundly without any preparation. , coupled with backward medical conditions, the post-earthquake epidemic also claimed many lives.

3. The largest earthquake in Europe

The largest earthquake in Europe was the 8.7-magnitude earthquake in Lisbon, Portugal. Back on November 1, 1755, which happened to be Halloween. Just as thousands of believers were praying to "be with God" in the church, a disaster came quietly. The earth beat wildly, six churches and 180,000 buildings collapsed, and tens of thousands of living lives disappeared in the shaking of the earth.

The shocked people had not yet woken up from the sudden blow. The second strong earthquake followed, causing a tsunami that rushed to the shore at a height of 30 meters. The entire city's buildings were destroyed in just 6 minutes. It was completely destroyed. However, greater catastrophe is yet to come. Another fire broke out in the urban area that was hit hard by the earthquake. Many precious materials were reduced to ashes in the fire, such as maps drawn by Portuguese navigators and the most complete literary and artistic works from the era of Queen Mary I in the world, which contributed to human civilization. Irreparable losses were caused.

Tips

Earthquake in Messina, Italy There was a saying in Italy: The most beautiful city in Italy is not Venice or Florence, but Messina on the island of Sicily. It is an ancient city with a history of more than 2,000 years. However, God seems to be jealous of its beauty. On December 28, 1908, a 7.2-magnitude earthquake occurred in Messina. 70,000 people were killed. The magnificent bell tower, church, and theater collapsed one after another. This beautiful city was razed to the ground in an instant. . The earthquake caused a tsunami with a wave height of 12 meters, which devastated cities on both sides of the Strait of Messina.

4. The largest earthquake in North America

A magnitude 9.2 earthquake occurred in Alaska, USA, on March 28, 1964. It was the largest earthquake in North American history. That day happened to be Good Friday, so it was also called the "Good Friday Earthquake." The earthquake permanently deformed the earth's crust as far away as Hawaii, damaging about 600 houses and killing 128 people. The tsunami caused by the earthquake affected the Pacific coast and island areas of the Americas, destroying an area of ??130,000 square kilometers.

Although the Alaska earthquake was very destructive, because the epicenter of the earthquake, Anchorage, was a newly built modern city, most buildings were designed with earthquake resistance requirements in mind, so almost no buildings were damaged during the earthquake. collapse of objects. Coupled with the small local population density, casualties and economic losses are relatively light. Therefore, after the earthquake, the city became a "live laboratory" for evaluating the seismic design of modern buildings.

Tips

1906 San Francisco Earthquake

San Francisco is a city prone to earthquakes. On April 18, 1906, a magnitude 7.8 earthquake struck San Francisco along the famous San Andreas Fault, where the Pacific Plate and the North American Plate meet. A fault zone about 400 kilometers long is formed on the ground. What is even more frightening is that the three days and nights of fires triggered by the earthquake burned down nearly 30,000 buildings and killed more than 3,000 people. Under the double blow of earthquake and fire, San Francisco experienced an unprecedented catastrophe, causing direct economic losses of US$500 million.

5. The largest earthquake in China

Looking at the map, Chayu, Tibet is just a small dot, and most people have never even heard of this name. However, 61 years ago, a major earthquake that shocked the world occurred here - the 8.6-magnitude Zayu-Medog earthquake on August 15, 1950, which was the largest earthquake in China's recorded history.

The earthquake area is located in the eastern section of the Himalayas. The area of ??damage reached more than 400,000 square kilometers. The furthest distance it could be felt was 1,200 to 1,300 kilometers. The area of ??hundreds of thousands of square kilometers in the Himalayas was instantly transformed beyond recognition. All the houses collapsed, the Brahmaputra River was cut into four sections by landslides, and blocked in many places. The earthquake killed more than 3,300 people in Tibet, and more than 1,500 people died in Assam, India.

Tibet Chayu-Medog 8.6 magnitude earthquake

Tips

Shanxi Hongdong-Zhaocheng earthquake

1303 September On March 17, an 8.0-magnitude earthquake occurred in Hongdong and Zhaocheng, Shanxi, which also caused secondary geological disasters such as collapses and landslides. Based on research on inscriptions, seismologists estimate that the earthquake killed 470,000 people. Not only that, the earthquake also severely damaged the agricultural lifeline of Zhaocheng and Hongdong counties - three irrigation systems, which dealt a fatal blow to local agricultural development.

6. The Great Hanshin Earthquake in Japan

As we all know, Japan is a country prone to earthquakes, but it relies on technology and financial resources to build buildings like steel and iron bones, and is known as One of the countries with the best earthquake-proof facilities in the world. Therefore, the 1994 World Conference on Disaster Reduction was held in Tokyo.

Tips

Kanto Earthquake, Japan

On September 1, 1923, a magnitude 7.9 earthquake occurred in Sagami Bay, 6,080 kilometers away from Tokyo, Japan. The earthquake destroyed 85% of the houses in Tokyo, 96% of the houses in Yokohama were razed to the ground, and the number of dead and missing people in the entire greater Tokyo area reached 140,000. This earthquake was the deadliest earthquake in Japan's history, which set off research on earthquake prediction and earthquake resistance in the Japanese seismological community.

However, before the excitement of the conference dissipated, disasters ensued.

On January 16, 1995, a magnitude 6.9 earthquake occurred in Hyogo Prefecture, Japan (later known as the Hanshin Earthquake or Kobe Earthquake), completely shattering Japan's "safety myth." The earthquake and subsequent fires caused the death of 5,502 people. Even buildings and infrastructure facilities that had undergone strict earthquake-resistant design and that the Japanese were proud of collapsed in large numbers. More than 100,000 buildings alone were destroyed. What's more serious is that the earthquake ruptured gas pipelines, causing raging fires. Since the design of the house contained more wooden structural materials, the post-disaster losses were even worse.

Tangshan Earthquake—A commemoration that cannot be forgotten (photo by Li Yongkang)

7. Tangshan Earthquake

On July 28, 1976, a 7.8-magnitude earthquake occurred in Tangshan, Hebei Province magnitude earthquake, Tangshan turned into ruins after the earthquake: traffic was paralyzed, houses collapsed, and ground cracks could be seen everywhere. Since the earthquake occurred in a densely populated urban area, and the earthquake occurred in the early morning, many people were hit while they were sleeping. Dead. The Tangshan earthquake caused more than 240,000 deaths and caused direct economic losses of more than 10 billion yuan. It was the earthquake with the largest casualties in the 20th century.

Tips

Ningxia Haiyuan Earthquake

On December 16, 1920, an 8.5-magnitude earthquake occurred in Haiyuan, Ningxia. It was another earthquake besides the Tangshan earthquake. Devastating earthquake. The earthquake occurred in the Shaanxi-Gansu-Ningxia region. More than 200,000 people died in this disaster. At that time, seismometers located in Tokyo, Japan, recorded surface waves generated by the earthquake that circled the earth twice. The affected area reached 5.21 million square kilometers, exceeding more than half of China. Its intensity shocked the seismology community at home and abroad.

Tangshan Earthquake Monument (photo by Li Yongkang)

The Tangshan Earthquake was a disaster, and it also brought more thoughts to China’s earthquake research. After this earthquake, our country's earthquake monitoring and forecasting has shifted from simple monitoring and forecasting to comprehensive prevention, and from scientific behavior to whole-society behavior under government organizations. This has played a certain role in promoting and promoting my country's earthquake monitoring and forecasting work!

8. The Wenchuan Earthquake

On May 12, 2008, an 8.0-magnitude earthquake occurred in the beautiful land of Yingxiu, Wenchuan, Sichuan. It was extremely destructive and had a wide impact. It affected almost half of Asia, with the three provinces of Sichuan, Gansu and Shaanxi suffering the most serious damage.

The Wenchuan earthquake

The Wenchuan earthquake caused huge losses to people's lives and property. As of September 2008, the earthquake caused 69,226 deaths and 17,923 missing people, bringing the total to 87,149 people and causing direct economic losses of 845.1 billion yuan. In addition, the earthquake occurred in the mountainous areas of Sichuan. There are many mountain fractures, rich water systems, and complex geological structures. The secondary geological disasters such as landslides, collapses, debris flows, and barrier lakes caused by the earthquake are complex and large-scale, thus aggravating the losses caused by earthquake disasters. .

The severely affected Beichuan County (photo by Li Yongkang)

Tips

Qinghai Yushu Earthquake

Yushu County is located in the southern part of Qinghai Province , on April 14, 2010, a 7.1-magnitude earthquake broke people's peaceful lives. Most of the local houses are civil structures, and 85% of the houses collapsed during the earthquake. In addition, the earthquake occurred at 7:49, so most people had not yet gotten up, resulting in heavy casualties. According to statistics, the earthquake caused 2,698 deaths, 270 missing, and direct economic losses of nearly 300 million yuan.

Qinghai Yushu Earthquake

Comparison of 9.577 and 222570

Comparison of Chile Earthquake and Haiti Earthquake

South America in 2010 was an eventful year land. There was an earthquake in Haiti on January 12 and an earthquake in Chile on February 27. In just over a month, the world was rocked by two major earthquakes. Comparing these two major earthquakes, we have an important discovery: the magnitude and epicenter intensity of the Chilean earthquake were much higher than those of the Haitian earthquake, but the death toll (577 people) was far smaller than the latter (222,570 people). Why is this?

Houses damaged in the earthquake in Haiti

Buildings that were damaged but not toppled by the earthquake in Santiago, the capital of Chile,

In addition to objective factors such as focal depth and epicenter location, In addition, a very important point is the earthquake prevention awareness of the Chilean government and people. Chile is located in an earthquake zone and has experienced frequent earthquakes in history. Since the 1960 earthquake, the Chilean government has had strict quality standards for buildings and relatively complete emergency measures. Therefore, although many buildings were damaged after the earthquake hit, they did not completely collapse.

In addition, the Chilean government also attaches great importance to people's earthquake prevention awareness publicity and education. On Robinson Crusoe Island, which was severely hit by the tsunami, the residents here usually participated in emergency escape drills, thus avoiding major casualties.

Tips

Chile, a "long and narrow country" prone to earthquakes

A series of volcanoes are distributed around the Pacific seabed, known as " "Pacific Ring of Fire", about 80% of the earth's earthquakes occur here, Chile happens to be located here. About 21% of the earthquakes recorded globally each year occur in Chile. Not only that, the boundary of the South American Pacific Plate where Chile is located is characterized by a small inclination angle of the subduction zone, so the frictional resistance is large and earthquakes with larger magnitudes are prone to occur.

Distribution map of earthquakes above magnitude 6.0 that occurred in Chile in the past 1570 years

10. Earthquake memory alarm bells ringing

The disaster caused by earthquakes is the most common disaster in the world. concerns. The frequent occurrence of major earthquakes has intensified human fear and made humans more worried about the earth beneath their feet. In fact, earthquakes are a natural disaster caused by the tectonic movement of the earth. There is no need for us to worry unfoundedly.

Earthquakes are natural disasters, but disaster prevention, disaster resistance, and disaster relief are human activities. As the saying goes, "If you are not prepared, you are not afraid of earthquakes, but if you are not prepared, you are afraid of earthquakes." While people understand its laws and reflect on its lessons, they must learn to fight against earthquake disasters and survive in disasters. Therefore, earthquake disaster prevention, monitoring and prevention, disaster prevention drills, self-rescue and mutual rescue are very important. With this kind of contingency plan mechanism, human beings will become proactive in the face of earthquake disasters and will not always be passively "beaten". We cannot count on God’s special favor when a disaster strikes. Disaster prevention and mitigation depend on ourselves.