Is There a Better Way to Measure Earthquakes?

A Northridge, Calif., bridge collapsed after a 1994 earthquake. A Northridge, Calif., bridge collapsed after a 1994 earthquake. spirit of america/ file photo

Two hundred years ago, Missouri was rocked by an earthquake so severe it made the Mississippi River flow backward and set off church bells in Boston more than 1,000 miles away. 

These details help convey the staggering scale and reach of what was a remarkable geologic event. Today, along with those accounts, we would also get a number: the magnitude of the earthquake. But that number is based on a logarithmic scale, and can be hard to grasp.  

Earthquakes aren't measured linearly, but in orders of magnitude. Which means a 6.1 magnitude quake like the one that shook Northern California over the weekend is about twice as big as the 5.8 earthquake that rattled Washington, D.C., in 2011—and nearly three times as strong in terms of the amount of energy it released. Some more context: The 7.0 earthquake that devastated Haiti in 2010 was eight times bigger than the Northern California quake, and released 22 times more energy. None of this jibes with the linear way people use numbers for most measurements in daily life.

Here's how Jesse Singal explained it over at New York magazine earlier this year: 

On a linear scale, we know that four is twice as big as two and eight twice as big as four. This is what a casual observer of earthquake magnitude scales would expect: that an earthquake of 6.0 packs twice the punch of a 3.0. But no! In reality, a 6.0 quake releases 31,622.776 times as much energy as a 3.0 quake. And a 7.0 releases 31.622 times as much energy as a 6.0.

So why do geologists talk about earthquakes this way? Why not use a scale that operates more like the ones used to measure weight, or length, or temperature, or any number of other natural phenomena?

The answer, it turns out, begins in outer space. "My amateur interest in astronomy brought out the term 'magnitude,' which is used for the brightness of a star," said Charles Richter—the scientist behind the well-known scale of the same name—in a 1980 interview.

The Richter Magnitude Scale is the method of earthquake measurement widely used in the  United States last century. Richter's idea was to track the amount of energy released by a quake the way an astronomer would measure the brightness of a star. Each number on the magnitude scale indicated an earthquake 10 times stronger than the last—which means the quake strength between each increment of one on the scale grows as the numbers climb. 

Today, earthquake magnitude is measured using another logarithmic system—usually called Moment Magnitude or just Magnitude—that's calibrated to the Richter Scale but can measure bigger quakes than the Richter Scale could. And while it might not be the most intuitive system, it's a far more useful one than a linear scale would be.

"The logarithmic magnitude scale also allows for comparison of earthquakes on relatively the same terms even though their impacts to society and structures ... can be quite different," Robert Williams, a geologist in the USGS Earthquake Hazards Program, told me in an email. "Compared to a linear scale the logarithmic scale provides an easy and more manageable way to represent this wide range of ground motion amplitude (often many orders of magnitude) and energy release for different quakes within an easily understandable range of numbers."  

Richter identified some of the reasons linear alternatives aren't really workable when he and colleagues established the scale in the 1930s. Again Singal: "If you rescaled things to a linear scale—such as how much energy is produced by a given quake—suddenly you’d be dealing with huge numbers for the big quakes. And huge numbers are another thing most people aren’t particularly good at grasping."

Besides, even though Richter apparently acknowledged that "logarithmic plots are a device of the devil," they're actually widely used, as geologist Williams reminded me. "Logarithmic scales are commonly used in other sciences, for example, the decibel scale in sound measurements and the pH scale in chemistry for rating acidity."

For now, at least, it seems we're stuck with charting earthquakes this way. And for those who find thinking logarithmically doesn't come naturally, USGS has a handy online calculator that shows just how different quakes compare with one another. ​

(Image via spirit of america / )

Stay up-to-date with federal news alerts and analysis — Sign up for GovExec's email newsletters.
Close [ x ] More from GovExec

Thank you for subscribing to newsletters from
We think these reports might interest you:

  • Sponsored by G Suite

    Cross-Agency Teamwork, Anytime and Anywhere

    Dan McCrae, director of IT service delivery division, National Oceanic and Atmospheric Administration (NOAA)

  • Data-Centric Security vs. Database-Level Security

    Database-level encryption had its origins in the 1990s and early 2000s in response to very basic risks which largely revolved around the theft of servers, backup tapes and other physical-layer assets. As noted in Verizon’s 2014, Data Breach Investigations Report (DBIR)1, threats today are far more advanced and dangerous.

  • Sponsored by One Identity

    One Nation Under Guard: Securing User Identities Across State and Local Government

    In 2016, the government can expect even more sophisticated threats on the horizon, making it all the more imperative that agencies enforce proper identity and access management (IAM) practices. In order to better measure the current state of IAM at the state and local level, Government Business Council (GBC) conducted an in-depth research study of state and local employees.

  • Sponsored by Aquilent

    The Next Federal Evolution of Cloud

    This GBC report explains the evolution of cloud computing in federal government, and provides an outlook for the future of the cloud in government IT.

  • Sponsored by LTC Partners, administrators of the Federal Long Term Care Insurance Program

    Approaching the Brink of Federal Retirement

    Approximately 10,000 baby boomers are reaching retirement age per day, and a growing number of federal employees are preparing themselves for the next chapter of their lives. Learn how to tackle the challenges that today's workforce faces in laying the groundwork for a smooth and secure retirement.

  • Sponsored by Hewlett Packard Enterprise

    Cyber Defense 101: Arming the Next Generation of Government Employees

    Read this issue brief to learn about the sector's most potent challenges in the new cyber landscape and how government organizations are building a robust, threat-aware infrastructure

  • Sponsored by Aquilent

    GBC Issue Brief: Cultivating Digital Services in the Federal Landscape

    Read this GBC issue brief to learn more about the current state of digital services in the government, and how key players are pushing enhancements towards a user-centric approach.


When you download a report, your information may be shared with the underwriters of that document.