When is an earthquake considered destructive and how is the strength of earthquakes calculated?

Arab Weather - Earthquakes are one of the most destructive natural phenomena, as the Earth's surface consists of tectonic plates that move under the surface of the Earth and oceans, and an earthquake occurs as a result of the discharge of energy stored in the Earth's crust, which leads to a sudden vibration of the Earth's surface and the occurrence of cracks.

Earthquakes vary in intensity; some are weak and not felt by people, while violent earthquakes can be destructive and cause great losses. The word "earthquake" is used to describe any seismic event, whether it is caused by natural activity or human activities such as nuclear explosions. In this article, we will learn how to calculate the strength of an earthquake and the types of earthquakes.

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Seismic Observatory

Types of earthquakes

• tectonic earthquakes

Tectonic earthquakes arise from the movement of tectonic plates at plate boundaries. There are three types of plate boundaries: transform, convergent, and divergent boundaries.

1. At transform boundaries, plates move sideways, causing them to slip.
2. At convergent boundaries, plates collide, breaking apart and forming mountain ranges and volcanoes.
3. At collision boundaries, plates collide, causing the Earth's crust to fracture and magma to flow, causing volcanic eruptions.

• Volcanic earthquakes

They occur as a result of volcanic activity when magma moves underground. Volcanic earthquakes are smaller than tectonic earthquakes but can indicate a possible volcanic eruption.

• artificial earthquakes

Resulting from human activities such as nuclear or chemical explosions, where rock explosions cause seismic waves.

Earthquake measurement: magnitude and intensity

Earthquakes are measured in two ways: magnitude and intensity.

1. The magnitude depends on the amount of energy released by the earthquake at the focus and is measured by seismometers.
2. The amount is expressed in Arabic numerals such as 4.8 or 9.0.

Richter scale

The Richter scale is the most famous way to measure the strength of earthquakes, developed by scientist Charles Richter in 1934. The scale is based on the amplitude of the largest recorded wave and takes into account the distance between the epicenter and the instrument.

• Classification of earthquakes according to the Richter scale

1. Microearthquake: Less than 1.0 to 2.9 on the Richter scale. No noticeable effects and occurs 100,000 times per year.
2. Minor earthquake: Between 3.0 and 3.9 on the Richter scale, felt by people but causing no damage, occurs 12,000 to 100,000 times per year.
3. Weak earthquake: between 4.0 and 4.9 on the Richter scale, felt by everyone and occurs 2,000 to 12,000 times per year.
4. Moderate earthquake: between 5.0 and 5.9 on the Richter scale, causes damage to weak buildings and occurs 200 to 2,000 times per year.
5. Strong earthquake: between 6.0 and 6.9 on the Richter scale, causes moderate damage in populated areas and occurs 20 to 200 times per year.
6. Major earthquake: between 7.0 and 7.9 on the Richter scale, causes extensive damage and casualties, and occurs 3 to 20 times per year.
7. Catastrophic earthquake: greater than 8.0 on the Richter scale, causing great destruction and loss of life, and occurring less than 3 times per year.

The most powerful destructive earthquakes in the last century

1. 1960 Chile Earthquake (9.5 Richter): The most powerful earthquake ever recorded struck Valdivia, Chile, followed by a massive 10-meter-high tsunami that destroyed entire villages.
2. 1964 Alaska Earthquake (9.2 Richter): Despite its enormous strength, it left 128 dead due to the small population of the area, and caused material losses amounting to $311 million.
3. 2004 Indian Ocean earthquake (9.1 Richter): More than 200,000 people were killed and 1.7 million displaced as a result of a giant tsunami that followed the earthquake.
4. 2011 Japan Earthquake (9.1 Richter): 20,000 deaths and over $210 billion in material losses.
5. 1932 Great Kanto Earthquake (8.4 Richter): Almost completely destroyed Tokyo, killing 142,000 people.
6. 2001 India earthquake (7.9 Richter): struck Gujarat state, killing 20,000 people and displacing a million others.
7. 1976 China earthquake (7.8 Richter): killed a quarter of a million people and reduced the city of Tangshan to rubble.
8. 2005 Pakistan earthquake (7.6 Richter): 73,000 people were killed in northern Pakistan and Kashmir and millions were displaced.
9. 2010 Haiti earthquake (7.0 Richter): killed 230,000 people and almost completely destroyed the capital, Port-au-Prince.

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