Magnitude vs. Intensity of Earthquakes

The whole Earth might not experience earthquakes, but they happen way more often than you think. We have seismographic networks that make it possible to measure these earthquakes by their intensity, release of energy, and magnitude.

Magnitude scales used to be based only on the waveform lengths that were recorded or the seismic wavelengths from one peak to another. Today, scientists have the technology to measure earthquakes by recording the physical effects of the earthquake instead of only measuring the waveforms.

How Do We Detect And Record Earthquakes?

When earthquakes shake the Earth, they are spreading energy through seismic waves. This is why a seismograph is the main technology used to measure how intense the earthquake was. The machine provides us with a visual graph of the motion caused by seismic waves.

Several seismographs around the world make up the seismograph network. This network can show us when an earthquake hits, where it hit, and how intense it was. 


An earthquake will have just one magnitude unit. It doesn’t depend on the location that the earthquake occurred or where the measurement is made. The Moment Magnitude Scale has the ability to detect earthquakes no matter where they are in the world.

The Moment Magnitude Scale was developed to capture all of the seismic waves from an earthquake worldwide. The scale is logarithmic, meaning it compares amplitudes instead of the strength or the energy of the earthquake. It makes it easier for us to differentiate between large and small earthquakes.

The Richter Scale

You’ve probably heard of the Richter Scale before. It uses a mathematical formula to compare the different sizes of earthquakes. However, it was replaced in 1970 because it mostly only worked for earthquakes that occurred in Southern California and ones that took place within 370 miles of the seismometer.

It also only calculated one type of wave created by earthquakes. It was replaced with the Moment Magnitude Scale. It is still used today, but for a different reason. 

We use the Richter Scale to predict future earthquakes and determine how damaging they might be.

Earthquake Magnitude Classes

Earthquakes are classified from minor to great depending on their magnitude. Classes can also tell us the measurement of the earthquake. Minor earthquakes have magnitudes between 3.0 and 3.9, while great earthquakes have magnitudes of 8.0 or higher.


We have a second way to measure earthquakes, and that is by their intensity. To measure the intensity of an earthquake, an on-the-ground description is used. It explains how severe the earthquake was shaking and the effects on make people in the area and their environment.

Intensity will vary based on the location of the earthquake to the epicenter. There is the potential to have multiple intensity measurements instead of just one magnitude measurement.

In the United States, we use the Modified Mercalli Intensity Scale. It was modified in 1931 from Giuseppe Mercalli’s intensity scale of 1902. 

The intensity scale ranges from I to X. I is shaking that isn’t felt, II and III are weak, IV is light, V is moderate, VI is strong, VII is very strong, VIII is severe, IX is violent, and X is extreme.

How To Prepare Your Home For Earthquakes?

If you live in the Pasadena or Los Angeles area that experiences frequent earthquakes, contact Seismic Safety at (626) 791-2300 to prepare your home or repair existing damage.