How did the Wenchuan Earthquake come about?

The structure of the earth is like an egg, which can be divided into three layers. The central layer is the "yolk" - the core; the middle layer is the "egg white" - the mantle; the outer layer is the "eggshell" - the crust. Earthquakes generally occur in the earth's crust. The earth is constantly rotating and revolving, and at the same time, the interior of the earth's crust is constantly changing. The resulting force causes the crustal rock layers to deform, fracture, and move, causing earthquakes.

An earthquake is a phenomenon in which the earth's internal medium locally ruptures sharply, generating seismic waves, thereby causing ground vibration within a certain range. An earthquake (earthquake) is a rapid vibration of the earth's surface. In ancient times, it was also called an earthquake. It is a natural phenomenon that often occurs on the earth, just like wind, rain, lightning, landslides, and volcanic eruptions. Earth vibration is the most intuitive and common manifestation of earthquakes. Strong earthquakes that occur under the sea or in coastal areas can cause huge waves, called tsunamis. Earthquakes are extremely frequent. About 5 million earthquakes occur around the world every year, which has a great impact on the entire society.

The place where seismic waves originate is called the focus. The vertical projection of the earthquake source on the ground. The point on the ground closest to the earthquake source is called the epicenter. It is the earliest part to receive vibration. The depth from the epicenter to the source is called the focal depth. Usually, earthquakes with a focal depth less than 70 kilometers are called shallow earthquakes, earthquakes with a depth of 70-300 kilometers are called intermediate earthquakes, and earthquakes with a depth greater than 300 kilometers are called deep earthquakes. For earthquakes of the same size, due to different focal depths, the degree of damage to the ground is also different. The shallower the earthquake source, the greater the damage, but the smaller the spread, and vice versa.

Destructive earthquakes are generally shallow earthquakes. For example, the focal depth of the 1976 Tangshan earthquake was 12 kilometers.

The place where the ground vibrations of a destructive earthquake is strongest is called the epicenter, and the epicenter is often the area where the epicenter is located.

The distance between a certain place and the epicenter is called the epicentral distance. Earthquakes with an epicenter distance less than 100 kilometers are called local earthquakes, earthquakes between 100 and 1,000 kilometers are called near earthquakes, and earthquakes greater than 1,000 kilometers are called telequakes. The farther away the epicenter is, the greater the impact and damage. Small.

The ground vibration caused by earthquakes is a complex movement, which is the result of the simultaneous action of longitudinal waves and transverse waves. In the epicenter, longitudinal waves cause the ground to move up and down. Transverse waves cause the ground to shake horizontally. Since longitudinal waves propagate faster and attenuate faster, transverse waves propagate slower and attenuate slower, so in places far away from the epicenter, you often cannot feel up and down beating, but you can feel horizontal shaking.

When a large earthquake occurs somewhere, a series of earthquakes often occur within a period of time. The largest earthquake is called a mainshock. The earthquake that occurs before the mainshock is called a foreshock. Earthquakes that occur after an earthquake are called aftershocks.

Earthquakes have certain spatiotemporal distribution patterns.

From a time perspective, earthquakes have a periodic phenomenon of alternating active periods and quiet periods.

From a spatial perspective, earthquakes are distributed in a certain belt shape, called seismic zones, mainly concentrated in the two major seismic belts of the Pacific Rim and the Mediterranean-Himalayas. The Pacific seismic zone concentrates almost 80% of the world's shallow source earthquakes (0 kilometers to 70 kilometers), all intermediate source earthquakes (70 kilometers to 300 kilometers) and deep source earthquakes, and the seismic energy released accounts for about 80% of all energy.

Earthquake Magnitude and Intensity

When earthquake research departments report earthquakes in a certain area, they often report that an earthquake of magnitude XX occurred, the intensity reached degree X, etc. The magnitude and intensity of an earthquake are not the same thing.

Magnitude

Magnitude refers to the size of an earthquake. It is a measure of the strength of an earthquake. It is determined by the amount of energy released by each seismic activity measured by a seismometer. Magnitude is usually represented by the letter M. The magnitude standard currently used in our country is the internationally used Richter scale, which is divided into 9 levels. Usually, earthquakes with a magnitude less than 2.5 are called minor earthquakes, earthquakes with a magnitude of 2.5-4.7 are called felt earthquakes, and earthquakes with a magnitude greater than 4.7 are called destructive earthquakes. For every 1.0 magnitude difference in earthquake magnitude, the energy difference is about 30 times; for every 2.0 magnitude difference, the energy difference is about 900 times. For example, a magnitude 6 earthquake releases as much energy as the atomic bomb the United States dropped on Hiroshima, Japan. A magnitude 7 earthquake is equivalent to 30 magnitude 6 earthquakes, or equivalent to 900 magnitude 5 earthquakes. The magnitude difference is 0.1 magnitude, and the energy released differs by an average of 1.4 times.

Earthquakes can be divided into the following categories according to their magnitude:

Weak earthquakes have magnitudes less than 3. If the source of the earthquake is not very shallow, it is generally difficult for people to detect this kind of earthquake.

The magnitude of the felt earthquake is equal to or greater than magnitude 3 and less than or equal to magnitude 4.5. Such earthquakes can be felt but generally do not cause damage.

The magnitude of a moderately strong earthquake is greater than 4.5 and less than 6. It is an earthquake that can cause damage, but the severity of the damage is also related to many factors such as focal depth and epicenter distance.

The magnitude of a strong earthquake is equal to or greater than 6. Among them, those with magnitudes greater than or equal to 8 are also called giant earthquakes.

Three elements of an earthquake:

Time of earthquake, magnitude, epicenter

Seismic intensity

Earthquakes of the same size will cause different damage It must be the same; the same earthquake causes different damage in different places. In order to measure the extent of earthquake damage, scientists have "produced" another "ruler" - earthquake intensity. On the China Earthquake Intensity Scale, people's feelings, general house earthquake damage levels and other phenomena are described, which can be used as the basic basis for determining the intensity. Factors that affect the intensity include magnitude, focal depth, distance from the focal point, ground conditions and stratigraphic structure.

Generally speaking, only in terms of the relationship between intensity, source, and magnitude, the larger the magnitude, the shallower the source and the greater the intensity. Generally speaking, after an earthquake occurs, the epicenter has the heaviest damage and the highest intensity; this intensity is called the epicenter intensity. The intensity of the earthquake gradually decreases as it spreads from the epicenter to the surrounding areas. Therefore, an earthquake has only one magnitude, but the damage it causes varies in different areas. In other words, an earthquake can be divided into several areas with different intensities. This is the same as when a bomb explodes, the degree of damage near and far away is different. The amount of explosive in a bomb is like the magnitude of the earthquake; the degree of damage caused by the bomb to different locations is like the intensity.

For example, on February 10, 1990, a magnitude 5.1 earthquake occurred in Changshu-Taicang. Some people said that it was magnitude 4 in Suzhou and magnitude 3 in Wuxi. This is wrong. No matter where it is, it can only be said that a 5.1-magnitude earthquake occurred in Changshu-Taicang. However, the earthquake intensity in Shaxi Town of Taicang was 6 degrees, in Suzhou it was 4 degrees, and in Wuxi it was 3 degrees.

Our country divides the intensity into twelve degrees. The impact and damage of earthquakes of different intensities are roughly as follows:

People cannot feel earthquakes less than three degrees, and only instruments can record them;

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In the third degree, people have feelings in the dead of night;

In the fourth and fifth degrees, people sleeping will wake up and the chandeliers will shake;

In the sixth degree, the utensils will fall over and the house will be slightly damaged;

In degrees 7 to 8, houses were damaged and cracks appeared on the ground;

In degrees 9 to 10, houses collapsed and the ground was severely damaged;

In degrees 11 to 12 Devastating damage;

For example, the 1976 Tangshan earthquake had a magnitude of 7.8 and an epicenter intensity of 11. Affected by the Tangshan earthquake, the earthquake intensity in Tianjin was 8 and Beijing had an intensity of 6 Degrees, and as far away as Shijiazhuang, Taiyuan, etc., there are only four to five degrees.

Earthquake Phenomenon

When an earthquake occurs, the most basic phenomenon is the continuous vibration of the ground, mainly obvious shaking.

People in extreme earthquake areas sometimes feel jumping up and down before they feel big shaking. This is because seismic waves are transmitted from the ground to the surface, and longitudinal waves arrive first. The transverse waves then produce large-amplitude horizontal shaking, which is the main cause of earthquake disasters. During the 1960 Chilean earthquake, the largest shaking lasted for 3 minutes. Disasters caused by earthquakes first destroy houses and structures, causing casualties of humans and animals. For example, in the 1976 Tangshan earthquake in Hebei, China, 70% to 80% of buildings collapsed, causing heavy casualties.

Earthquakes also have a great impact on the natural landscape. The main consequence is faults and cracks in the ground. The surface faults of major earthquakes often extend for tens to hundreds of kilometers, and often have obvious vertical and horizontal offsets, which can reflect the characteristics of tectonic changes at the source (see the Nobi Earthquake and the San Francisco Earthquake). But not all surface fractures are directly linked to the movement of the earthquake source. They may also be due to secondary effects caused by seismic waves. Especially in areas with thick surface sedimentary layers, ground cracks often appear on the edges of slopes, river banks, and on both sides of roads. This is often due to topographic factors. Shaking without support on one side causes the topsoil to loosen and crack. The shaking of the earthquake causes the surface soil to sink, and the shallow groundwater will be squeezed and rise to the surface along the ground fissures, causing the phenomenon of sand blasting and water eruption. Major earthquakes can cause local terrain changes, uplift or subsidence. Cracked urban and rural roads, twisted railroad tracks, and broken bridges. In modern cities, water outages, power outages, and communication disruptions occur due to ruptured underground pipes and cut cables. Leakage of gas, toxic gases and radioactive substances can lead to fires and secondary disasters such as toxic and radioactive pollution. In mountainous areas, earthquakes can also cause landslides and landslides, often burying villages and towns. Collapsed rocks blocked rivers and formed earthquake lakes upstream. During the Great Kanto Earthquake in Japan in 1923, a mudslide occurred in Kanagawa Prefecture, sliding down the valley as far as 5 kilometers.

Two major seismic zones in the world

Pacific Rim Seismic Zone: distributed around the Pacific Ocean, like a huge garland, separating the continents from the ocean.

Mediterranean-Himalayan seismic zone: From the Mediterranean Sea to the east, one branch passes through Central Asia to the Himalayas, then southward through the Hengduan Mountains of my country, through Myanmar, and turns eastward in an arc to Indonesia. Extending from Central Asia to the northeast to Kamchatka, the distribution is relatively scattered.

China's seismic activities are mainly distributed in 23 seismic zones in five regions.

These five regions are: ① Taiwan Province and its adjacent waters; ② Southwest region, mainly Tibet, western Sichuan and central and western Yunnan; ③ Northwest region, mainly in Gansu Hexi Corridor, Qinghai, Ningxia, and the northern and southern foothills of Tianshan; ④ North China Areas, mainly on both sides of the Taihang Mountains, the Fenwei River Valley, the Yinshan-Yanshan area, central Shandong and the Bohai Bay; ⑤ Guangdong, Fujian and other places on the southeast coast. my country's Taiwan Province is located in the Pacific Rim Seismic Belt, Tibet, Xinjiang, Yunnan, Sichuan, Qinghai and other provinces and regions are located in the Himalayan-Mediterranean Seismic Belt, and other provinces and regions are in related seismic zones.

Occurrence and types of earthquakes

Earthquakes are divided into two categories: natural earthquakes and artificial earthquakes. In addition, earthquakes may also occur under certain special circumstances, such as large meteorites impacting the ground (meteorite impact earthquakes). There are many reasons for vibrations on the earth's surface. According to the causes of earthquakes, earthquakes can be divided into the following types:

1. Tectonic earthquakes

Due to the cracking and dislocation of rocks deep underground, the energy accumulated over a long period of time is rapidly released and spreads in all directions in the form of seismic waves. The shaking of the house caused by the ground shaking is called a tectonic earthquake. This type of earthquake occurs the most frequently and is the most destructive, accounting for more than 90% of earthquakes in the world.

2. Volcanic earthquakes

Earthquakes caused by volcanism, such as magma activity, gas explosions, etc., are called volcanic earthquakes. Volcanic earthquakes are only possible in volcanic active areas, and these earthquakes account for only about 7% of the world's earthquakes.

3. Collapse earthquake

An earthquake caused by the collapse of the roof of an underground cave or mine is called a collapse earthquake. Such earthquakes are relatively small in scale and infrequent. Even if they occur, they often occur in limestone areas with dense caves or mining areas with large-scale underground mining.

4． Induced earthquakes

Earthquakes caused by activities such as reservoir storage and oil field water injection are called induced earthquakes. This type of earthquake only occurs in certain reservoir areas or oil field areas.

5. Artificial earthquakes

Ground vibrations caused by underground nuclear explosions, explosive blasting, etc. are called artificial earthquakes. Artificial earthquakes are earthquakes caused by human activities. For example, vibrations caused by industrial blasting and underground nuclear explosions; high-pressure water injection in deep wells and water storage in large reservoirs increase the pressure on the earth's crust and sometimes induce earthquakes.

The place where seismic waves originate is called the earthquake source. The vertical projection of the earthquake source on the ground is called the epicenter. The depth from the epicenter to the source is called the focal depth. Usually, earthquakes with a focal depth less than 70 kilometers are called shallow earthquakes, earthquakes with a depth of 70-300 kilometers are called intermediate earthquakes, and earthquakes with a depth greater than 300 kilometers are called deep earthquakes. Destructive earthquakes are generally shallow earthquakes. For example, the focal depth of the 1976 Tangshan earthquake was 12 kilometers.

Earthquake Expertise

The fluctuations we are most familiar with are observed in water waves. When a stone is thrown into a pond, the water surface is disturbed, and ripples expand outward from the point where the stone enters the water. This wave train is caused by the movement of water particles near the water wave. However, the water does not flow in the direction of the waves; if a cork floated on the surface, it would bounce up and down but would not move from its original position. This disturbance is transmitted continuously by the simple back and forth motion of the water particles, from one particle to the preceding particle. In this way, the water waves carry the energy of the water surface broken by the stone impact to the edge of the pool and stir up waves on the shore. Earthquake motion is quite similar. The shaking we feel is the vibration of elastic rocks produced by the energy of seismic waves.

Assuming that an elastic body, such as a rock, is struck, two types of elastic waves will be generated and propagate outward from the source.

The physical properties of type 1 waves are just like sound waves. Sound waves, and even ultrasonic waves, are transmitted in the air by alternating squeezing (push) and expansion (pull). Because liquids and gases can be compressed just as well as solid rocks, the same types of waves can travel through bodies of water, such as oceans and lakes, as well as through solid Earth. During an earthquake, this type of wave travels outward from a fracture at equal speed in all directions, alternately squeezing and stretching the rock they pass through, with its particles moving forward and backward in the direction in which these waves travel. In other words In other words, the motion of these particles is perpendicular to the wave front. The amount of forward and backward displacement is called amplitude. In seismology, this type of wave is called a P wave, or longitudinal wave, and it is the first wave to arrive.

Unlike air, which can be compressed but not sheared, elastic rock allows the second type of wave to propagate by causing the object to shear and twist. The second arriving wave produced by an earthquake is called an S wave. When an S wave passes through, the rock behaves quite differently than it does during P wave propagation. Because S waves involve shear rather than compression, the motion of the rock particles is transverse to the direction of migration. These rock movements can be in a vertical or horizontal plane, and they are similar to the lateral movement of light waves. The simultaneous existence of P and S waves gives the seismic wave train a unique combination of properties, making it different from the physical manifestations of light waves or sound waves. Because shear motion is not possible within liquids or gases, S waves cannot propagate in them. The distinct properties of P and S waves can be used to detect the presence of fluid zones deep within the Earth.

S wave has polarization phenomenon, and only those light waves that vibrate laterally in a specific plane (up and down, horizontal, etc.) can pass through the polarizing lens. The light waves passing through are called plane polarized light.

Sunlight passing through the atmosphere is unpolarized, that is, there is no preferred transverse direction in which the light waves vibrate. However, refraction of the crystal or through specially manufactured plastics such as polarized eyes can turn unpolarized light into plane polarized light.

When S waves pass through the Earth, they are refracted or reflected when they encounter tectonic discontinuous interfaces, polarizing their vibration direction. When the rock particles that produce polarized S waves move only in the horizontal plane, they are called SH waves. When rock particles move in the water plane containing the direction of wave propagation, this S wave is called SV wave.

Most rock, unless it is forced to vibrate at too high an amplitude, has linear elasticity, that is, the deformation due to an applied force varies linearly with the applied force. This linear elastic behavior is called obeying Hooke's law, named after Robert Hooke (1635~1703), a British mathematician who was a contemporary of Newton. Similarly, rocks will deform proportionally to increasing forces during an earthquake. In most cases, the deformation will remain in the linear elastic range and the rock will return to its original position at the end of the shaking. However, important exceptions sometimes occur during earthquake events. For example, when strong shaking occurs in soft soil, permanent deformation will remain. After wave deformation, the soil cannot always be returned to its original position. In this case, the earthquake intensity Less predictable.

The movement of elasticity provides excellent insights into how energy changes as seismic waves pass through rock. The energy associated with spring compression or extension is elastic potential, and the energy associated with the movement of spring components is kinetic energy. The total energy at any time is the sum of elastic energy and kinetic energy. For an ideal elastic medium, the total energy is a constant. At the position of maximum amplitude, all energy is elastic potential energy; when the spring oscillates to the intermediate equilibrium position, all energy is kinetic energy. We have assumed that no friction or dissipative forces are present, so once the reciprocating elastic vibration begins, it will continue at the same amplitude. This is of course an ideal situation. During an earthquake, the friction between moving rocks gradually generates heat and dissipates some of the fluctuating energy. Unless new energy is added, like a vibrating spring, the earth's vibrations will gradually cease. Measurements of seismic wave energy dissipation provide important information about the inelastic properties of the Earth's interior. However, in addition to frictional dissipation, there are other factors that contribute to the gradual weakening of seismic vibrations with increasing propagation distance.

Since the wave front of a sound wave propagates as an expanded spherical surface, the sound it carries weakens as the distance increases. Similar to the expanding water waves in a pond, we observe that the height or amplitude of the water waves also gradually decreases outward. The amplitude decreases because the initial energy spreads wider and wider and causes attenuation, which is called geometric diffusion. This type of dispersion also weakens seismic waves that pass through Earth's rocks. Unless there are special circumstances, seismic waves propagate farther away from the source, the more their energy attenuates.

Famous Earthquakes

Top Ten Earthquakes in China

Serial Number Earthquake Name Date Time Magnitude (Ms) Epicenter Intensity Focal Depth (Km)

1 Xingtai Earthquake, Hebei Province, 1966.3.8 05:29:14.0 6.8 IX 10

Dongwang, Ningjin, Hebei Province, 1966.3.22 16:19:46.0 7.2 X 10

2 Tonghai Earthquake, Yunnan Province, 1970.1 .5 01：00：37.0 7.7 ：18.3 7.1 IX 14

5 Haicheng Earthquake in Liaoning Province 1975.2.04 19:36:06.0 7.3 IX 12

6 Longling Earthquake in Yunnan Province 1976.5.29 20:23:18.0 7.3 IX 24

1976.5.29 22:00:22.5 7.4 IX 20

7 Hebei Tangshan Earthquake 1976.7.28 03:42:53.8 7.8 XI 12

8 Sichuan Songpan Earthquake 1976.8.16 22:06:46.2 7.2 IX 24

1976.8.23 11:30:10.0 7.2 VIII 23

9 Taiwan 921 Earthquake 1999.9.21 01:47 7.3 8

10 Wenchuan Earthquake in Sichuan 2008.5.12 14:28:04.0 8.0 An earthquake measuring 8.5 on the Richter scale occurred on March 28 (09:09 on the 29th, Beijing time). This is one of the eight strongest earthquakes in human history since 1900. The following is the basic situation of the eight major earthquakes (arranged by magnitude):

1. Chile Earthquake (May 22, 1960): 8.9 on the Richter scale (later revised to 9.5 on the Richter scale). It occurred in the waters off central Chile and triggered tsunamis and volcanic eruptions. The earthquake caused 5,000 deaths and 2 million people homeless.

2. The Great Alaska Earthquake in the United States (March 28, 1964): 9.2 on the Richter scale. This triggered a tsunami, killing 125 people and causing property damage of US$311 million. Strong earthquakes were felt in most parts of Alaska, Canada's Yukon Territory and Colombia.

3. The Great Alaska Earthquake (March 9, 1957): 9.1 on the Richter scale, occurred in the waters near Andrea Island and Unak Island in Alaska, USA. The earthquake caused the Vesevedov volcano, which had been dormant for 200 years, to erupt and trigger a 15-meter-high tsunami, affecting as far away as Hawaii Island.

4. (Tie) Indonesian earthquake (December 26, 2004): 9.0 on the Richter scale, occurred in Aceh Province, located on the island of Sumatra, Indonesia.

The tsunami triggered by the earthquake swept through Sri Lanka, Thailand, Indonesia, India and other countries, leaving about 300,000 people missing or dead.

4. (tied) Russian earthquake (November 4, 1952): 9.0 on the Richter scale. The tsunami caused by the earthquake affected the Hawaiian Islands, but there were no casualties.

5. The Great Ecuador Earthquake (January 31, 1906): 8.8 magnitude on the Richter scale, occurred along the coasts of Ecuador and Colombia. The earthquake triggered a powerful tsunami, killing more than 1,000 people. The earthquake was felt along the coast of Central America, San Francisco and Japan.

6. (tied) Indonesian earthquake (March 28, 2005): 8.7 on the Richter scale. The epicenter was located in the sea north of Sumatra, Indonesia, not far from the location of the 9.0-magnitude earthquake three months ago. . So far, 1,000 people have died, but it has not caused a tsunami.

6. (Tie) The Great Alaska Earthquake in the United States (February 4, 1965): 8.7 on the Richter scale. The earthquake triggered a 10.7-meter-high tsunami that swept across the entire Shumanya Island.

7. The Great Earthquake in Tibet, China (August 15, 1950): 8.6 on the Richter scale. More than 2,000 houses and temples were destroyed. India's Brahmaputra River suffered the most losses, with at least 1,500 people killed.

8. (tied) Russian earthquake (February 3, 1923): 8.5 on the Richter scale, occurred in Kamchatka Peninsula, Russia.

9. (Tie) Indonesia Earthquake (February 3, 1938): 8.5 on the Richter scale, occurred in the waters near Banda, Indonesia. The earthquake triggered tsunamis and volcanic eruptions, causing heavy losses to people and property.

10. (tied) Russia’s Kuril Islands Earthquake (October 13, 1963): 8.5 on the Richter scale, affecting Japan, Russia and other places.

11. China Sichuan Wenchuan Earthquake (May 12, 2008): 8 on the Richter scale. The epicenter was located in Wenchuan County, Aba Prefecture, and affected most of China and overseas. There were heavy casualties to people and property.

★Earthquake Self-Rescue Guide

Aftershocks are very likely after an earthquake, and the location of aftershocks may not be very close to the earthquake source. Therefore, learning to self-rescue is one of the most important measures after an earthquake.

When an earthquake occurs, it is crucial to have a clear mind and a calm attitude. Only by being calm can it be possible to use the earthquake knowledge you have learned in daily life to judge the size and distance of an earthquake. Recent earthquakes often start with an up-and-down bump, followed by a side-to-side sway. Teleshocks have less up and down bumps, and mainly swing from side to side, with crisp sound and small vibrations. Generally, there is no need to flee for small earthquakes and distant earthquakes.

The latest self-rescue advice: Don’t hide under the table

Among the ten items of shock-absorbing knowledge in Japan’s "Earthquake Manual", the first item clearly states "Hide under sturdy furniture" Down". Therefore, Japanese teachers firmly believe that the best way is to "hide under the table". This idea is based on the premise that the Japanese earthquake will end in tens of seconds and the ceiling will not fall.

When the ceiling of a building collapses due to a strong earthquake, furniture such as tables and beds will be crushed. If a person hides in it, the consequences will be disastrous. If a person hides next to the furniture in a low posture, the furniture may be damaged by the collapsing objects first. The strength allows the people on the side to gain living space.

If you encounter an earthquake while driving, you should get out of the car as soon as possible. Many people who died in the parking lot during the earthquake were crushed to death in the car. The people between the two cars were not injured at all. hurt. When a strong earthquake occurs, if you are in a parking lot, do not stay in the car to avoid the falling ceiling crushing the car and causing injury; you should hide next to the car in a lying position to prevent the falling ceiling from pressing on the car. A direct impact on the human body may form a "living space" and increase the chance of survival.

School shock absorbers

When you are on the playground or outdoors, you can squat down and protect your head with your hands, and be careful to avoid tall buildings or dangerous objects.

Don't go back to the classroom.

Evacuation should be organized after the earthquake.

Don’t jump off the building! Don't stand outside the window! Don't go to the balcony!

Classes should be held outdoors when necessary.