# What is Richter scale?

A seismograph measures and records the ground movement of an earthquake in a series of lines on a graph.

The Richter scale, officially called the “Richter Magnitude Scale”, is a numerical value used to measure the strength of earthquakes. It is a logarithmic scale based on the amplitude of waves recorded by a seismograph. This means that each integer increase in the scale corresponds to an absolute increase by a factor of ten. Earthquakes measured at less than 2.0 on the Richter scale are not very serious and can barely be measured, let alone felt. An earthquake is generally considered to be much more serious and is felt by most people once it reaches around 5.0.

what the numbers mean

The 12 levels of the Mercalli scale are written in Roman numerals.

Each number on the Richter scale is equal to a tenfold increase in the magnitude of an earthquake. In other words, an earthquake measuring 6.0 on this scale has a magnitude ten times greater than a 5.0 earthquake. An integer increase also indicates that about 31 times more energy was released during an earthquake.

Magnitude Class Effects 2.0 or less Micro Cannot be felt. 2.1 – 3.9 Minor Many are not felt, although those at the higher end may be. It can cause very little damage. 4.0 – 4.9 Light Can be felt. General tremor, but usually only minor damage. 5.0 – 5.9 Moderate May cause light to moderate damage to structures. 6.0 – 6.9 Strong Can cause significant damage, especially in populated areas. 7.0 – 7.9 Major Causes serious and widespread damage. 8.0 – 9.9 Excellent Extremely destructive. It can completely destroy entire communities.

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It is theoretically possible to have an earthquake of 10.0 or stronger, although this has never been recorded. Such an earthquake would be classified as massive and would cause devastation over a very wide area.

Magnitude vs. damage

While higher numbers generally indicate more damage, the Richter scale cannot be used as a direct measure of an earthquake’s destructive force.

It is important to distinguish between the magnitude of an earthquake and the damage it causes. While higher numbers generally indicate more damage — and these earthquakes are often described in terms of damage — the Richter scale cannot be used as a direct measure of an earthquake’s destructive force. Many factors contribute to the amount of destruction and loss of life caused by an earthquake, including the population of the area, the type of building, the type of earthquake, and the depth of the earthquake. A 5.0 magnitude earthquake hitting a densely populated area with old or poorly constructed buildings, for example, is likely to cause more damage than a 7.0 earthquake that occurs in a remote region with few people or structures.

How earthquakes are recorded

Even quakes which rate low on the Richter scale can cause significant damage to homes.

Seismographs record the magnitude of an earthquake. These devices detect waves traveling through the earth and portray them as a series of lines that move up and down. Greater movement in the earth creates more extreme differences — or amplitude — in the lines that are recorded, creating a visual representation of the earthquake’s waves.

The Richter scale is based on measuring the intensity of this difference. Higher numbers come from more extreme recorded patterns. In most cases, the seismograph is not actually at the epicenter of an earthquake, however; it’s often at least some distance away from the place where the quake actually occurs. Based on this distance, the machine is specially calibrated so that scientists can determine what the magnitude that it recorded would have been if it was actually located at the center of the quake.

limitations

The Richter scale measures the intensity of earthquakes.

News releases about an earthquake can be confusing, as evaluating the current magnitude often takes time. A preliminary value is usually released to provide an approximation for the power of the quake, but this does not always match the official value released after the data is fully analyzed.

The Richter Magnitude Scale was developed in 1935, and it does have some additional limitations. Earthquakes with a magnitude above about 8.0 cannot be measured very accurately using this scale. While there is no upper limit, measurements are not as accurate because of how they are made. The scale uses the size of the largest waves recorded by a seismograph, which ignores the smaller but steadier waves created by a quake. These smaller types of waves are more likely to cause structural damage during an earthquake since they tend to occur for longer periods of time.

Alternative Scales

To accurately record Great earthquakes, a system called the moment magnitude scale (MMS) is often used. This scale is based on all waves created in an earthquake, including those that may take almost two minutes to reach the device that records them. Although most current earthquakes are actually measured by this scale, they are still frequently described as registering some number on the Richter scale.

Another way to measure earthquakes is with the Mercalli Intensity scale, which measures how the surface of the earth reacts to the movement. This scale has 12 levels, written in Roman numerals, and was created to be easier for the average person to understand. For example, an earthquake that rates a III on the Mercalli scale feels similar to the vibrations caused when a large truck passes by, and can be felt, but is not always recognized as an earthquake. A quake rated VI is clearly felt, moves furniture around, and can even knock some plaster from walls, but does not cause major damage. A IX causes considerable damage, and may cause buildings to partially collapse; a XII, the highest rating, indicates a quake that throws items into the air and causes major destruction.