Differences between Mercalli Scale and Richter Scale

Comparison Article

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Differences between Mercalli Scale and Richter Scale

Two primary scales used to measure earthquakes are the Mercalli scale and the Richter scale. While both assess the impact of seismic events, they do so by measuring different parameters. The Mercalli scale evaluates the intensity of an earthquake based on its observable effects, whereas the Richter scale measures the seismic energy released at the earthquake's source, known as its magnitude.

The Modified Mercalli Intensity (MMI) scale is a qualitative measurement that describes the effects of an earthquake in a specific location. It relies on eyewitness accounts and observations of damage to structures to assign an intensity level. This scale is particularly useful for understanding the impact on populated areas and for assessing historical earthquakes that occurred before the invention of modern seismic instruments.

In contrast, the Richter scale provides a quantitative measure of an earthquake's magnitude. Developed in 1935 by Charles F. Richter and Beno Gutenberg, it is a logarithmic scale based on data from seismographs. A key feature of the Richter scale is that for each whole number increase, the measured wave amplitude increases by a factor of 10, and the energy released increases by approximately 31.6 times. This allows for a more objective comparison of the relative size of different earthquakes.

Comparison Table

Category	Mercalli Scale	Richter Scale
What it Measures	Intensity: The observable effects and damage caused by an earthquake at a specific location.	Magnitude: The amount of energy released at the earthquake's source (epicenter).
Basis of Measurement	Subjective observations from people and assessment of damage to buildings and the environment.	Objective instrumental measurement of seismic waves recorded by seismographs.
Type of Scale	Linear, descriptive scale using Roman numerals from I (not felt) to XII (catastrophic destruction).	Logarithmic, quantitative scale using Arabic numerals. Each whole number represents a tenfold increase in wave amplitude.
Value Consistency	Varies from place to place for the same earthquake, generally decreasing with distance from the epicenter.	A single magnitude value is assigned to the entire earthquake.
Data Collection	Relies on eyewitness reports and damage surveys, which can take time to collect after an event.	Calculated quickly after an earthquake using data from seismic networks.
Primary Use	Assessing the impact on inhabited areas, for historical earthquake analysis, and for informing emergency response and building codes.	Providing a rapid, scientific measure of an earthquake's size, allowing for objective comparison of different seismic events.

Venn diagram comparing Differences between Mercalli Scale and Richter Scale

Development and Limitations

The precursor to the modern Mercalli scale was first developed by Giuseppe Mercalli in the late 19th and early 20th centuries. The version commonly used today is the Modified Mercalli Intensity Scale, developed in 1931. A primary limitation of the Mercalli scale is its subjectivity, as personal accounts can vary and building damage is dependent on construction quality and local ground conditions. It is also less effective in sparsely populated or uninhabited areas where observable effects are minimal.

The Richter scale was created to provide a more scientific and consistent measure of earthquake size. It was originally designed for measuring moderate-sized earthquakes in Southern California within a specific distance from a particular type of seismograph. For this reason, modern seismology often uses other scales, such as the Moment Magnitude Scale (Mw), which provides a more accurate measure of the total energy released by large earthquakes. While the Richter scale is still widely mentioned in news reports, the Moment Magnitude Scale is the standard used by seismologists today for large quakes.