Explore Earthquakes

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Why do earthquakes and tsunamis occur?

On September 12, 2016, a 5.8-magnitude earthquake, the strongest ever recorded on the Korean Peninsula, struck Gyeongju. The following year, a 5.4-magnitude earthquake struck Pohang. The earthquakes caused damage such as collapsed walls, tilted buildings, and damaged vehicles. In the past, Korea was considered safe from earthquakes, but recently, earthquakes have become stronger and more frequent. However, historical documents such as “Samguk Sagi”(History of the Three Kingdoms), “Goryeosa”(History of Goryeo), and “Joseon Wangjo Sillok” (Annals of the Joseon Dynasty) indicate that over 1,700 earthquakes have occurred on the Korean Peninsula, making it hard to consider Korea a safe zone from earthquakes. So, why do earthquakes occur? As shown in the image below, when continuous pressure is applied to the Earth’s crust, it bends. Eventually, when it can no longer withstand the stress, it breaks. This is called a ① . When a fault forms, vibrations of the ground are transmitted to the surface, and this is called an  ② .

Damage Caused by Earthquakes

Principle of Faults

Earthquakes occur not only along faults but also due to volcanic activity or the collapse of underground caves. Earthquakes can also occur beneath the sea. A ③ is a phenomenon in which sudden changes in sea level, caused by undersea earthquakes, landslides, volcanic eruptions, or meteorite impacts, generate waves that travel long distances. A tsunami is also known as a seismic sea wave. In the deep ocean, tsunami waves are only a few centimeters high, but as they reach shallow waters, they rise dramatically and become dangerous. What should we do if a tsunami occurs? If you feel an earthquake near the sea or notice the water suddenly receding, a tsunami may occur. In such cases, quickly move away from the coast and head to a designated tsunami evacuation area or a sturdy building at least three stories high. Although modern science and technology cannot predict earthquakes, they can help us prepare for them. By learning earthquake preparedness steps in advance, with earthquake monitoring agencies immediately sending warnings after the first tremor, and by constructing earthquake-resistant buildings, we can prepare for earthquakes.


The 2004 tsunami that struck the Indian Ocean coast near Thailand.

When an earthquake occurs, follow these steps.

1. Take cover under a sturdy table to protect yourself.
2. Turn off the gas and electricity, and open a door to secure an exit.
3. Use the stairs to evacuate outside. 
4. Move away from buildings and walls to avoid falling debris.

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The Size of an Earthquake

Comparing Magnitude and Intensity

The size of an earthquake is determined by both its magnitude and intensity. A higher number on either scale indicates a stronger earthquake. Magnitude refers to an earthquake’s energy and is expressed using Arabic numerals. The Richter scale, invented by American scientist Charles Richter in 1935, is commonly used. Each increase of 1 in magnitude means an earthquake’s energy increases by about 30 times. In contrast, intensity refers to the amount of ground shaking felt at a specific location. It is expressed using Roman numerals. Intensity is greater the closer it is to the earthquake’s epicenter.

Intensity I
A tremor too weak for humans to feel but detectable by seismographs.
Intensity II

Slight swaying of hanging objects, felt by a few people.

Intensity III

Shaking is noticeable indoors, similar to a passing truck.

Intensity
Stationary cars shake.


Intensity V
Almost everyone feels the shaking, dishes and windows may break.

Intensity VI
Everyone feels the earthquake, heavy furniture moves, and cracks may appear in walls.
Intensity VII
People run outdoors in fear, drivers feel the shaking.


Intensity VIII
Windows fall from frames, structures like pillars, monuments, and walls collapse.
Intensity IX

All buildings are damaged, the ground cracks, and underground water pipes are destroyed.

Intensity X

The ground splits, and railroad tracks bend.


Intensity XI
Bridges collapse, and deep fissures appear on the ground.


Intensity XII
Objects are thrown into the air, and waves appear on the ground’s surface.


Are magnitude 1 and intensity I the same size of an earthquake?
④

Inferring the Reasons Why Earthquakes Are Perceived Differently in Size

Why did people in various locations feel the Pohang earthquake differently? Write your answer.
⑤

Earthquake News

Earthquake News: When the earthquake struck Pohang, it caused significant damage, including collapsed walls and tilted buildings. In Gwangju, Busan, and Jeju, many people felt the shaking and contacted fire departments with inquiry calls. In Seoul and Gyeonggi, some people indoors noticed the tremors.

What should you do during an earthquake? Choose the action that should NOT be taken.
⑥

(a) Take the elevator to move

(b) Go to the coast

(c) Protect your head with a bag during evacuation.

(d) Take cover under a table when shaking occurs.
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Volcanic Zones and Seismic Zones

Activity 1

Please follow the instructions and assemble the educational kit in the order specified.

Activity 2: Compare and Observe Volcanic Zones and Seismic Zones

Regions with many volcanoes are called volcanic zones, and regions with frequent earthquakes are called seismic zones. Observe the locations of volcanic zones and seismic zones on the map, and compare their positions.

Do the locations of volcanic zones and seismic zones match? Which regions have the most volcanic and seismic activity?
⑦

Finding the Causes of Volcanoes and Earthquakes

The Earth’s surface is composed of approximately 10 tectonic plates, as shown on the map below. Each plate moves at a rate of 1–10 cm per year in the direction indicated by the arrows. The plates may collide, move apart, or shift past each other. Observe the positions, shapes, and movement directions of the plates, and think about how the regions with frequent volcanic and seismic activity relates to the locations of the plates. Write your thoughts.
⑧
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