Friday, April 18, 2008

It's been a while since I've taught Geol 100

Some people referred to that class as "rocks for jocks" and as much as I hate stereotyping, I have to yield to that one with the idea that we had some bright athletes. I had a student who couldn't find the US on a world map because it wasn't labelled though... so sad.

So I'm sure this event will be blogged to death but, having a geology background, how could I pass it up? This is of course in response to the earthquake that occurred in south-eastern Illinois at 4:30ish this morning. I can't think of one place on this earth that isn't free from potential natural disaster. If you can let me know. With several people shocked at the possibility of earthquakes happening in the Midwest, I feel I must let you know that yes, Illinois can have earthquakes. So here are some quick Q&A for you - I promise not to bog you down with too much detail as I'm sure I lose a few readers once I throw up a few graphs and maps anyway:

I thought the Midwest would be earthquake free... - nope, sorry, and the world is not coming to an end (at least not at the moment I don't think). If you really want to find a place earthquake-free then use this map as a guide.
For those who need to know, these units are given in %g where g equals the acceleration of gravity (9.8m/s/s)... Never mind, red = bad and white = good.

Who's at fault? - many are familiar with the New Madrid seismic zone for the major earthquakes that have come from it but today's earthquake was from the Wabash Valley seismic zone which is a northern extension of the New Madrid zone.

How often can we expect this to happen? - while earthquakes are hard to predict, past history can give as a better idea of frequency. From the USGS site, "the zone had at least eight prehistoric earthquakes over the past 20,000 years with estimated magnitudes ranging from about 6.5 to 7.5, based on geologic evidence". To give you an idea, today's quake was in the 5.2-5.4 range depending on who measured it.

5.2-5.4? What do the numbers mean? - again from the USGS website, "Magnitude scales, like the Richter magnitude and moment magnitude, measure the size of the earthquake at its source. On the Richter scale, an increase of one unit of magnitude (for example, from 4.6 to 5.6) represents a 10-fold increase in wave amplitude on a seismogram or approximately a 30-fold increase in the energy released. " If you ever hear about Intensity scales (which you don't so much these days) then those refer to the varying degrees of damage done and is unique to an individual earthquake.

You most likely have to click on this to be able to read it but this should give you a general feel for what to expect with different magnitude earthquakes.

When they say the epicenter was located at Mt. Carmel, IL, 7 miles below the surface, what does that mean exactly? - The epicenter is a vertical projection or the point directly above the exact location (focus) along the fault line (underground) where an earthquake originates. So really when they say the epicenter is 7 miles underground, they are using the wrong terminology.

Yes I know Illinois is not this mountainous... but you get the point.

And a current question brought up by my sis-in-law...

Can animal behavior be used as an indicator of an impending earthquake? - well, some say yes but it basically remains a mystery. Some amazing stories, for example, Chinese officials evacuating a city with one million people prior to a 7.3 magnitude earthquake using predictions based on animal behavior - it seems some people put a lot of stock into monitoring critters.

Apparently Neal could feel the effects of the quake but no damage done - I can't believe I missed it... every geologist should experience at least a little one... oh well.

And I feel I must mention for those wondering, no I don't have a lot of background in seismology although I did take a Sedimentology and a Geophysics course where I did use actual seismo equipment if that counts. Just imagine me and some other budding geologists on BYU campus smacking a sledge hammer onto a concrete slab to create our seismic activity... those were fun days. Naw, I chose the way of the envirogeochemist (ya I know that is a mouthful)...


  1. Oh my. I'm happy to see that other people have just a little geek in them as well... Very enlightening diagrams. Bored in SC? ha ha.

  2. Thanks for sharing the info. I really found it interesting to know what the chances of another earthquake in our area are.

  3. Wow, you sure know your stuff. Thanks! I'm sad you didn't feel anything :(

  4. Fascinating. I'm glad to live far away from any RED zones :) Thanks for clarifying all of this for us!


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