How does earthquake magnitude differ from intensity? When you talk about earthquakes, their magnitude, and intensity are two crucial concepts that come up in discussions.
Earthquakes are natural occurrences that can endanger lives and cause extensive property damage.
However, in seismic science, magnitude and intensity have different meanings and functions, despite their shared connection to earthquake magnitude.
So, with regard to earthquakes, what distinguishes intensity from magnitude?
Magnitude refers to the size of the quake at any point from the epicenter, whereas intensity measures the wave’s strength, which loses power with distance from the center.
How Does Earthquake Magnitude Differ from Intensity?
The magnitude is essentially a quantitative measure of the energy released where the earthquake begins.
And magnitude indicates the size of the earthquake.
Let’s discuss these concepts in detail:
More about the Magnitude of Earthquake
The magnitude of an earthquake is a single value that refers to the earthquake’s size. It is measured using a seismometer that picks up the vibrations of the quake as they move through the Earth.
Each wave recorded reflects the amplitude of the vibrations, or the amount of movement.
The recorded waveform amplitudes are considered a better reflection of the size of the earthquake than measures of magnitude.
But, it is important to know that there are concerns that measures of magnitude underestimate the true size of earthquakes.
Fact: These days, scientists use amplitude to measure the strength of earthquakes.
More about the Intensity of Earthquake
An earthquake’s intensity is reflected by a collection of values, each one specific to a location within the geographic area around the quake’s epicenter.
It is a measure of the shaking which varies from place to place depending on the geology and makeup of the surface material.
Because of the differences between one location and another, intensity is measured using scales with qualitative terms that describe the earthquake’s observable effects.
Such scales were in use before modern seismometers and have been developed since to account for:
- The ground movement accelerating
- The distance from the source
- The local geology
Differences between Earthquake Magnitude and Intensity
Magnitude and intensity are therefore two separate and very different measures, each providing data on different features of earthquakes.
Magnitude measures the size of the quake and remains unchanged regardless of how far from the epicenter the measure is taken.
Intensity measures the shake which decreases with distance from its center.
Conceptual Differences
Magnitude records how much energy an earthquake puts out and is recorded as a single, continuous measure by seismometers.
Magnitude
Magnitude scales were developed under the premise that all waveform amplitudes were equivalent.
But, the method was later established as not reliably providing the full picture particularly when describing large earthquakes.
However, the most famous magnitude scale was first developed by Charles Richter to get a quantitative ranking of the earthquake’s size.
It revolved around knowing the distance from the seismometer to the earthquake’s center and observing the maximum signal amplitude recorded.
Intensity
On the other hand, intensity is the amount of shaking, and is considered a more accurate measure.
It is determined by the earthquake’s effect on population, structures and the natural environment and their distance from the fault.
Fact: The Richter scale calculates magnitude from a mathematical formula using the largest amplitude wave recorded and the seismometer’s distance from the epicenter.
Measurement Methods and Scales
The Richter scale was the first widely used earthquake measurement. The Richter scale was developed in 1934, but today another scale is often preferred.
The Moment Magnitude Scale, Mw, remains relevant no matter what the size of the quake and is applied globally as the standard.
The first scale widely adopted for measuring the intensity of earthquakes was developed in 1902 by Giuseppe Mercalli. It was modified in 1931 to become the Modified Mercalli Intensity Scale.
This scale, the MMI scale, uses Roman numerals to avoid confusion with the Richter Scale was one of several developed over the centuries.
Fact: The MMI is not mathematical like the Richter but is composed of descriptions of damage that match intensity levels more like the Saffir-Simpson Hurricane Wind Scale.
Measuring Different Characteristics of Earthquakes
Magnitude and intensity measure different characteristics of earthquakes.
One is a measure of the energy released at its source as tectonic forces trigger movement.
But, the other considers the impact of the movement on humans and structures at locations moving away from the epicenter.
Despite measuring different aspects of the earthquake both scales ultimately describe its size.
The Richter Scale is considered a more scientific method than the descriptive MMI scale or its predecessor, the Rossi-Forel scale, which as early as 1873 had ten such intensity levels.
Because the descriptions can be modified to suit local conditions, the Rossi-Forel is still used in some parts of the world.
The scale also measures the impact against previous experiences of similar-sized quakes, like the potential damage a hurricane can cause.
This perhaps makes this kind of scale more useful for communicating warnings and reporting.
An Important Consideration
Another way to calculate the intensity of an earthquake to rank it according to its impact on the planet’s surface is to find its Energy Magnitude, Me.
The difficulty with this method is that the energy earthquakes release is not released at one single frequency but many and all need to be mathematically factored in for accuracy.
Role in Earthquake Reporting and Analysis
As it happens, there is no shortage of scales that rank earthquakes whether by magnitude or intensity.
However, over the years the public has come to recognize the terminology of the Richter Scale.
Also, with modern live feed recordings at least some have an idea of the impact when an earthquake is assigned a high numerical value.
However, as the analysis of events surrounding Hurricane Katrina revealed, when warnings are given, not everyone understands them.
Specifically, how the rankings and classifications work and underestimate the level of danger.
An Important Consideration
Imminent earthquake warnings are perilously short if they happen at all.
Also, perhaps people get used to the threat when they live in earthquake zones, but as our planet is reacting to changes in its climate, we can expect more natural disasters.
Fact: Creating preparedness means educating the public about the intensity scales and their descriptions of damage, which should be more relevant than the mathematical scales.
Importance of Understanding Magnitude and Intensity
Understanding more about the magnitude and intensity of earthquakes is important because it helps in many different ways.
For instance:
Earthquake Preparedness
Worldwide there are many campaigns educating vulnerable populations about disaster preparedness.
It reduces damage, injury and loss of life. People are encouraged to plan and practice what to do to optimize warnings and survive.
It includes being familiar with the scales and understanding that the ranking is also a reflection of the event’s impact on daily living.
Also, when used in a warning, it is also an indication of the risk to property and life.
Emergency Response and Infrastructure Planning
Many city authorities now have some sort of disaster preparedness plan covering their emergency response such as opening evacuation routes.
Many have upgraded regulations for new buildings and infrastructure with earthquake intensities firmly in mind.
In future earthquakes, these modern structures will stay standing for longer because of their innovative designs and materials.
Scientific Research and Earthquake Monitoring
During the last decade seismic monitoring has dramatically improved with revolutionary advances in sensing equipment.
The quality of data has consequently improved, along with the technology to manipulate and model it.
Monitoring near global coverage and the chances of surviving an earthquake are higher than ever.
Fact: Around 500,000 earthquakes are detected each year, only a fifth are felt but these caused over 50% of the fatalities attributed to natural disaster.
Public Awareness and Communication
The importance of public awareness and communication before, during and after an event, can never be understated.
All preparedness campaigns stress:
- Keeping in touch
- Following the news
- Monitoring local updates on social media
All this is to be ready to move only when and if told to.
Takeaway
How does earthquake magnitude differ from intensity? The size and intensity of an earthquake are two separate but related notions in seismic research.
The magnitude of an earthquake is a numerical representation of the amount of energy released at the epicenter.
However, intensity considers elements like distance, geological conditions, and human perception to zero in on the effects felt at the surface of the Earth.
Having a firm grasp on these two concepts is essential for scientists and engineers to better analyze seismic hazards.
