Earthquakes are one of the most powerful and unpredictable natural phenomena that occur on our planet. They can cause devastating consequences, such as loss of life, destruction of infrastructure, and economic setbacks. To assess and communicate the strength and impact of earthquakes, scientists use two essential measurements: magnitude and intensity. While these terms are often used interchangeably, they represent distinct aspects of an earthquake’s characteristics.
Magnitude: The Measure of Earthquake’s Energy
Magnitude is a quantitative measurement that represents the energy released at the earthquake’s source. It is a logarithmic scale, meaning that each whole number increase on the scale indicates a tenfold increase in amplitude and approximately 31.6 times more energy release. The most commonly used magnitude scale is the Richter scale, which was developed in 1935 by Charles F. Richter and Beno Gutenberg.
The Richter Scale and Examples
The following table illustrates Richter Scale and other parameters.
| Richter Magnitude | Description | Example |
| Less than 2.0 | Micro | Not felt by people |
| 2.0 – 2.9 | Minor | Felt, but rarely causes damage |
| 3.0 – 3.9 | Minor to Light | Noticeable shaking, minimal damage |
| 4.0 – 4.9 | Light to Moderate | Felt by many, minor to moderate damage to weak structures |
| 5.0 – 5.9 | Moderate to Strong | Can cause significant damage to poorly constructed buildings |
| 6.0 – 6.9 | Strong to Major | Can cause severe damage in populated areas |
| 7.0 – 7.9 | Major | Serious damage over large areas |
| 8.0 – 8.9 | Great | Devastating in areas several hundred miles across |
| 9.0 and above | Mega | Catastrophic destruction in a wide region |
- Example: The 2010 Haiti earthquake had a magnitude of 7.0, classifying it as a “Major” earthquake. It resulted in an estimated 230,000 deaths and caused extensive damage to buildings and infrastructure.
Earthquake Intensity: Effects on the Earth’s Surface
While magnitude measures the earthquake’s energy at the source, intensity gauges the effects experienced at specific locations on the Earth’s surface. The intensity of an earthquake is evaluated using various intensity scales, with the most widely used being the Modified Mercalli Intensity (MMI) scale.
The MMI Scale and Intensity Levels
The following table illustrates MMI scale and intensity levels.
| MMI Intensity | Description | Effects |
| I | Not Felt | Not felt by people |
| II | Weak | Felt by a few people, no structural damage |
| III | Weak to Light | Felt by many, no significant damage |
| IV | Light | Noticeable indoors, negligible damage to buildings |
| V | Moderate | Felt by everyone, some damage to weak structures |
| VI | Strong | Felt by all, moderate damage to average buildings |
| VII | Very Strong | Damaging in well-built structures, slight damage to ordinary buildings |
| VIII | Severe | Severe damage to poorly designed buildings |
| IX | Violent | Destructive in all constructions, heavy objects thrown into the air |
| X | Extreme | Some structures destroyed, considerable damage to most buildings |
| XI | Violent | Rail tracks bent, underground pipelines damaged |
| XII | Catastrophic | Almost total destruction, objects thrown into the air |
- Example: The 1906 San Francisco earthquake is estimated to have had an intensity of approximately IX on the MMI scale. It caused severe damage to poorly constructed buildings, resulting in significant destruction and loss of life.
Key Differences between Magnitude and Intensity
- Measurement Focus: Magnitude quantifies the energy release at the earthquake’s source, while intensity assesses the effects experienced at specific locations.
- Scale Type: Magnitude is measured on a logarithmic scale, while intensity is measured on a descriptive scale, such as the MMI scale.
- Range of Values: Magnitude values typically range from less than 2.0 to over 9.0, while the MMI scale ranges from I to XII.
- Standardization: Magnitude measurements are relatively consistent regardless of the observer’s location, while intensity measurements can vary depending on the distance from the earthquake’s epicenter.
- Impact Assessment: Magnitude helps seismologists categorize earthquakes based on their energy release, while intensity assists in understanding the level of damage and potential impact on communities.
Magnitude and intensity are both crucial measurements used to comprehend and communicate the characteristics of earthquakes. Magnitude provides a standardized way of representing an earthquake’s energy release, while intensity helps us understand the effects it produces on the Earth’s surface and the potential impact on structures and communities.
