Shake your groove thing? … or happy anniversary?

Today is the 199th anniversary of the big New Madrid quake. A big deal? Well, the New Madrid Quakes of 1811-1812 were some of the strongest quakes ever recorded in North America. FEMA is taking the opportunity to urge Americans to be prepared for quakes in their area.

Don’t know the likelihood of an earthquake in your part of the country?

Start here on the USGS Earthquake Hazards page.

Scroll down. On the left side of the page, you’ll find links to regional seismic lab sites. There will be one that covers your area of the country.

Or, scroll down some more. You’ll see a link under the EARTHQUAKES heading for “Info by State.” You can find maps that show faults and rifts where you live. You can determine what the USGS figures the odds are of a quake in your area. And you can see the odds of a quake of a given magnitude happening. Certainly, all of this is scientific estimation at best, but even the worst scientific guess beats being caught flat footed. I can tell you, the odds of my friends in California getting shaken up are better than mine – at any given magnitude. Bless their hearts. Yet, according to the U.S. Geological Survey, New Mexico is not inactive seismically. Small tremors happen here quite frequently. This is not to say that a big one can’t happen, only that it hasn’t in a while. But when you compare our hazard maps with those from the New Madrid Zone, or you look at a seismic hazard map where you can see New Mexico hazards in relation to what’s shaking in California, you can get a better feel for what the dangers are like.

When you start reading about earthquakes, you’ll see two scales used to convey the intensity of the quake: Richter and Mercalli. You’ve probably heard of the Richter scale, since it’s the most common measure you hear in the media.

This from the USGS website:

“The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.”

Kinda puts thing in better perspective, doesn’t it? Except that the Richter scale only addresses the magnitude of the quake event itself and it doesn’t touch on the intensity of an earthquake’s impact on the people who are in it. For most of us, we’d be hard pressed to tell you the difference between a 4.2 and a 4.6 if we had shaken our way through it. For a scale that communicates the power of a quake in terms most people immediately “get,” we turn to the Modified Mercalli Intensity Scale. If you’re like most folks, you haven’t heard of the Mercalli scale. Even so, it provides a real-world basis for people to understand how big a given quake must have been.

Again from the USGS:

“The effect of an earthquake on the Earth’s surface is called the intensity. The intensity scale consists of a series of certain key responses such as people awakening, movement of furniture, damage to chimneys, and finally – total destruction. Although numerous intensity scales have been developed over the last several hundred years to evaluate the effects of earthquakes, the one currently used in the United States is the Modified Mercalli (MM) Intensity Scale. It was developed in 1931 by the American seismologists Harry Wood and Frank Neumann. This scale, composed of 12 increasing levels of intensity that range from imperceptible shaking to catastrophic destruction, is designated by Roman numerals. It does not have a mathematical basis; instead it is an arbitrary ranking based on observed effects. The Modified Mercalli Intensity value assigned to a specific site after an earthquake has a more meaningful measure of severity to the nonscientist than the magnitude because intensity refers to the effects actually experienced at that place.

I highly recommend spending some time cruising the USGS website. It’s packed with tons of useful information – and it’s more than just rocks and earthquakes. It’s the planet. And it’s seriously cool and useful stuff.  Just for grins and chuckles, as of this writing, the last reported earthquake in New Mexico was Tuesday, December 14, 2010 at 9:47 a.m. local time. It was a magnitude 2.9 whose epicenter was 65 miles (105 km) northwest of Santa Fe. Food for thought.

As always, thanks for reading.

~ L.

References

U.S. Geological Survey. “The Modified Mercalli Intensity Scale.” Retrieved from: http://earthquake.usgs.gov/learn/topics/mercalli.php

U.S. Geological Survey. “The Richter Magnitude Scale.” Retrieved from: http://earthquake.usgs.gov/learn/topics/richter.php

Maps: usgs.gov

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2 Responses to “Shake your groove thing? … or happy anniversary?”

  1. Slamdunk Says:

    Good information. It always surprises me about how much at risk some of the central states are.

  2. Domain Names Says:

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