How Earthquakes are Measured

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Map showing the future seismic activity areas in the USA.

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The horrific earthquake that devastated parts of Turkey and Syria on February 6, 2023, was the strongest, biggest, and baddest earthquake that region has seen in a long time, and as of this writing, 37,600 deaths have been confirmed. This earthquake had, “a magnitude of at least Mw 7.8, and a maximum Mercalli intensity of X (Extreme) (Wikipedia).”

When I read that line, I realized that measuring earthquakes goes far beyond what those of my generation used to refer to as the Richter scale (used to measure earthquakes between 1935 and 1970). There are many different methods for measuring earthquakes and as the previous quote indicates, earthquakes need to be measured in magnitude, intensity, and energy release to make them comparable. I will say right up front that this is a very complex topic and I will just barely crack the lid on it. For more information, I suggest going to the following website: https://www.usgs.gov/programs/earthquake-hazards/ .

When the Earth shakes, it sends out waves of energy from the point of origin of the movement. This movement is measured through a network of sensitive devices called seismographs that produce a digital graphic image of the movement. The peak of the movement causes the highest points, or amplitude, on the graph, called a seismogram. This is the magnitude of the earth movement or earthquake—a measure of the size of the waves on the seismograph.

Magnitude is measured in whole numbers and decimal fractions. So, the recent earthquake had a magnitude of 7.8. It is important to note that the scale is logarithmic. That means the difference between a 6.8 and 7.8 magnitude is not one, but ten times greater. To visualize that, assume that a 6.8 magnitude quake produces a graph with an amplitude (height of the graph wave) of ten inches. The 7.8 quake amplitude would therefore be 100 inches.

The US Geological Survey (USGS) has a calculator on the previously mentioned website where you can put in values and see the differences. In their example, an 8.7 earthquake is not three times bigger on the seismogram than a 5.8 quake, but rather 794 times larger due to the logarithmic scale.

That is part one of the story. Magnitude, energy release and intensity are all related, but should not be confused with each other. According to the USGS, “While each whole number increase in magnitude represents a tenfold increase in the measured amplitude, it represents 32 times more energy release.” For instance, in the USGS example, the magnitude of the two quakes may be 794 times different, but the 8.7 event is 23,000 times stronger than the lesser quake. In other words, it would take 23,000 5.7 earthquakes to equal the energy released by the 8.7 event.

Since Charles Richter built his models and equations in the 1930s, there has been a lot of advancement worldwide in earthquake science. It became increasingly clear over time that Richter’s methods, while accurate, were limited to a local area of California and did not represent very large earthquakes well. A more universal model was needed. Since 1970, a scale called the Moment Magnitude (Mw) has been used as it is global in application. Rather than measurements taken from a seismograph, this metric measures the amount of slip along the fault multiplied by the area that the slippage covers, and becomes a truer measure of the quake’s energy release and size. However, this takes time to calculate and so the magnitude, taken from the seismograph, is often the first thing reported to the public.

The final measure is called the Modified Mercalli intensity. This is a much more subjective approach intended to determine the actual impact of the earthquake (the actual shaking) on humans and resources and has no mathematical basis. It is ranked on a scale, using Roman numerals, from I-X with I being essentially undetectable without equipment to X (as in the Turkey-Syria quake) which has extreme damage.

If all the energy released from all the earthquakes that have occurred in the past 112 years was added together, it would not equal the energy that would be released in a single 10.x event (remember the logarithmic nature of the scale) which would be 2,000 times stronger than the recent earthquake. Let’s hope that Nature never decides to throw that tantrum.

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Help Idaho Wildlife

When we traveled across the state in October 2017, most of the vehicles we saw using the wildlife management areas did not have wildlife plates. Buying wildlife plates is a great way for non-hunters and hunters alike to support wildlife-based recreation like birding.

C'mon folks, let's help Idaho's wildlife by proudly buying and displaying a wildlife license plate on each of our vehicles! 

See below for information on Idaho plates. Most states have wildlife plates so if you live outside Idaho, check with your state's wildlife department or vehicle licensing division for availability of state wildlife plates where you live. 

And tell them that you heard about it from Nature-track.com!

Wildlife License Plates

Idaho Wildlife license plates provide essential funding that benefits the great diversity of native plants and wildlife that are not hunted, fished or trapped—over 10,000 species or 98% of Idaho’s species diversity. Game species that share the same habitats (such as elk, deer, antelope, sage-grouse, salmon, trout) also benefit from these specialty plates.

No state tax dollars are provided for wildlife diversity, conservation education and recreation programs. Neither are any revenues from the sale of hunting or fishing licenses spent on nongame species. Instead, these species depend on direct donations, federal grants, fundraising initiatives—and the Idaho Wildlife license plates.

Both my vehicles have Bluebird Plates. I prefer the bluebird because the nongame program gets 70 percent of the money from bluebird plates, but only 60 percent of the money from elk and trout plates - 10 percent of the money from elk plates supports wildlife disease monitoring and testing programs (to benefit the livestock industry) and 10 percent from cutthroat plates supports non-motorized boat access.

Incidentally, in 2014, the Idaho Legislature denied the Department of Fish and Game the ability to add new plates or even to change the name of the elk and cutthroat plates (very specific) to wildlife and fish plates, a move that would have allowed for changing images occasionally and generating more revenue. It would seem that they believe that we Idahoans don't want a well funded wildlife program.

I think it is time we let the Legislature know that Idahoan support wildlife funding and that we would like to see these generic plates come to fruition.