Earthquake

An earthquake is any sudden shaking of the ground caused by seismic waves passing through rocks on Earth. Seismic waves occur when some form of energy stored in the earth’s crust is suddenly released , usually when suddenly contracting rock masses fracture. Earthquakes occur most often along geologic faults , narrow areas where rock masses move past each other. The world’s major faults are located on the fringes of the huge tectonic plates that make up the earth’s crust . The science that studies earthquakes is known asseismology . The term earthquake is closely related to the movements of the earth.

Characteristics of an earthquake

The main characteristics of an earthquake are the following:

• They are sudden movements of earth that happen in the inner layer of the earth.
• They happen naturally and spontaneously .
• They are caused by the collision of tectonic plates .
• They move by means of vibrations that travel through the earth’s crust.
• They can be measured by means of scales .
• Depending on their intensity, earthquakes are capable of causing great destruction and death .
• They have no mechanism to predict them.

History

The history of earthquakes until the seventeenth century was scarce because there was no understanding of the process that originated them. Many thought that they were due to divine punishments for man’s bad behavior. The first known earthquake occurred in China in 1777 BC In Europe , the first known earthquake occurred in 580 BC From this century onwards, stories about earthquakes began to be found

Types of earthquake

There are three different types of earthquakes classified according to the depth of the focus of the energy release, in this way we have:

• Superficial : their focus does not go beyond 70 kilometers in depth, they are the ones that cause the greatest damage because their impact with the earth’s surface is greater. The hypocenter in these earthquakes are located between 10 and 25 kilometers in depth .
• Intermediate : the focus occurs at a depth of between 70 and 300 kilometers deep.
• Deep : they have their focus outside the limits of the lithosphere , this means more than 300 kilometers deep and are imperceptible by people.

Measurement

The measurement of earthquakes is done by means of a device called a seismograph whose function is to measure the vibration produced by the earth when tectonic plates collide. This instrument gives us the magnitude and duration of the earthquake and records the surface waves that travel on the surface of the earth and the central waves that travel through the earth from the depth of the earth.

Intensity

Intensity is measured using the Richter scale and measures the amount of energy released by a tremor or an earthquake. It was developed by Charles F. Richter and is also useful for predicting tsunami formation . It can also be measured using the Mercalli scale, which measures damage and not intensity.

Magnitude of an earthquake

The magnitude of an earthquake represents the seismic energy that is released when an earthquake occurs. It is measured on a scale that grows in power and each point of increase means a greater increase in energy. This scale is called Richter and tells us then that:

• Less than 3.5 : not felt, but registered
• 3.5 – 5.4 : felt, but only causes minor damage.
• 5.5 – 6.0:  May cause slight damage to buildings.
• 6.1 – 6.9:  can cause severe damage in heavily populated areas.
• 7.0 – 7.9 : This is a major earthquake that has the force to do serious damage.
• 8 or greater: it  is considered a great earthquake and causes total destruction to nearby communities due to its force.

Earthquakes can also be measured with the Mercalli scale and this is expressed by means of Roman numerals, where intensity XII is the highest and in which there is total destruction of towns or lands, seas and rivers.

Causes

The causes that cause an earthquake are the landslides of the tectonic plates that overlap or collide and this is known as a fault. When the plates collide, they produce a release of energy or seismic waves that produce a sudden reorganization of the materials of the earth’s crust .

Consequences

Earthquakes have major consequences on land and people. They produce physical and structural damage that is difficult to solve. The loss of human life, the economic damage and the social and emotional devastation that they can cause make them rank first in natural disasters. In addition to this, they have the ability to produce tsunamis , huge waves that affect the coasts, causing the loss of human lives and commercial activities .

How to prevent an earthquake

To date, there is no method to determine when an earthquake is going to happen as they occur spontaneously without any prior warning. Thanks to the study of movements and plates , it is known which are the places most prone to earthquakes and for this reason, earthquake prevention plans and systems are developed . One of the methods that has been used lately is the SCIGN system that is responsible for monitoring the movement of tectonic plates by means of GPS . The best thing is to establish emergency plans and constructions based on earthquake systems. to avoid possible catastrophes.

How earthquakes spread

Earthquakes propagate through seismic waves produced by the friction of tectonic plates, which can produce anything from a small shake to a catastrophe. The point at which an earthquake originates is called the focus and the epicenter is the point that is located farthest toward the earth’s surface.

Examples

The most intense earthquake to hit the earth occurred in Chile on May 22, 1960, had a magnitude of 9.5 on the Richter scale and was perceived throughout the southern cone of America . 1,655 people died, 3,000 were injured and 2,000,000 people were made homeless. In addition, it caused a tsunami that caused extensive damage in Hawaii , Japan , the Philippines and the United States .

Another major earthquake was in Alaska on March 27, 1964. It lasted a whopping 4 minutes and produced a tsunami with waves of up to 5 meters. It produced changes in the soil and caused the sand to go into a liquid state

In 2004, there was a major earthquake in Indonesia with a magnitude of 9.1 on the Richter scale . Thousands of people died and countries like Africa and South Asia were affected . It lasted 10 minutes and is one of the longest in history, so much so that it managed to make the entire planet vibrate an inch.