What is Richter Scale? How it works?

The Richter magnitude scale is a scale that assigns earthquakes a number between 1 and 10 in order of increasing intensity.

Earthquakes are one of the most dangerous disasters that humans have to face. It can be as small as barely being noticed, or large enough to destroy cities. However, the fact is that most earthquakes are actually not even noticeable. There are millions of other small quakes that happen everyday, which humans don’t even realize. According to the U.S. Geological Survey, there are as many as 1.3 million earthquakes in a year that humans can feel. Of the million that are noticeable, the majority take place in remote areas far from people and are often so low in intensity that most people would not notice.

There are many reasons why earthquakes occur. They range from meteor impacts and volcanic eruptions, to man-made events like mine collapses and underground nuclear tests. However, the most common reason for earthquakes is the shifting of the Earth’s tectonic plates.

However, what’s more important is how we can be warned of future earthquakes, so that we may be better prepared and that we may avoid most damage; hence, a seismograph. A seismograph or seismometer is an instrument that measures the motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources.

The seismograph has a weight hanging on a spring. Hence, it is sensitive to up-down motions of the earth. The spring and weight are suspended from a frame that moves along with the earthʼs surface. As the earth moves, the relative motion between the weight and the earth can be recorded to create the history of the earth’s motion. Changes in motion can be used to indicate the chances and intensity of an earthquake.

In order to classify how intense and dangerous an earthquake is, many various scales were developed. One of these, and perhaps the most popularly known today, is the Richter scale. The Richter scale was developed by Charles Francis Richter in 1935 in collaboration with Beno Gutenberg. Both were from the California Institute of Technology, and the scale was originally intended to be used in only in a particular study area in California, and only on seismograms recorded on the Wood-Anderson torsion seismograph. However, eventually the scale was developed into a worldwide accepted standard.

The Richter magnitude scale assigns the number on the basis of how much energy is released during the earthquake. It assigns earthquakes a number between 1 and 10 in order of increasing intensity. Hence, 1 is an earthquake that cannot be felt by a person, while 10 is an earthquake that can cause total destruction.

The scale is a base-10 logarithmic scale, which means that an earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0, and corresponds to a 31.6 times larger release of energy. While the scale is usually considered to label from 1 to 10, and 0 being the basis to which the energy is being compared, the truth is that the scale does not actually have a lower limit. Many sensitive modern seismographs now routinely record quakes with negative magnitudes.

Today, many scientists actually prefer the more modern Moment Magnitude Scale (MMS). However, the Richter scale still remain the most popularly known by the general public.

Classification of earthquakes as per the Richter magnitude scale:

Magnitude Level

Category

Effects

Earthquakes per year

Less than 2.0

Micro

Microearthquakes, not felt, or felt rarely by sensitive people.

Several million per year

2.0–2.9

Minor

Felt slightly by some people. No damage to buildings.

Over one million per year

3.0–3.9

Minor

Often felt by people, but very rarely causes damage.

Over 100,000 per year

4.0–4.9

Light

Noticeable shaking of indoor objects and rattling noises. Felt by most people in the affected area. Slightly felt outside. Generally causes none to minimal damage.

10,000 to 15,000 per year

5.0–5.9

Moderate

Can cause damage of varying severity to poorly constructed buildings. At most, none to slight damage to all other buildings. Felt by everyone. No Casualties.

1,000 to 1,500 per year

6.0–6.9

Strong

Damage to a moderate number of well built structures in populated areas. Earthquake-resistant structures survive with slight to moderate damage. Poorly-designed structures receive moderate to severe damage. Felt up to hundreds of miles/kilometers from the epicenter. Death toll can range from none to 25,000, depending on location.

100 to 150 per year

7.0–7.9

Major

Causes damage to most buildings, some to partially or completely collapse or receive severe damage. Well-designed structures are likely to receive damage. Can be felt up to 250 km away from epicenter. Death toll can range from none to 250,000, depending on location.

10 to 20 per year

8.0–8.9

Great

Major damage to buildings, structures likely to be destroyed. Will cause moderate to heavy damage to sturdy or earthquake-resistant buildings. Damaging in large areas. Felt in extremely large regions. Death toll can ranges from 1,000 to 1 million.

One per year

9.0 and greater

Great

Near or at total destruction - severe damage or collapse to all buildings. Heavy damage and shaking extends to distant locations. Permanent changes in ground topography. Death toll usually over 50,000.

One per 10 to 50 years

How Does the Richter Scale Work?

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