http://www.anss.org/

How do we get these pretty and protective colors to warn us about nasty earthquakes and other seismic nastiness?

SEISMOLOGY, OF COURSE!!!!

Without seismological data, our buddies in Southern Illinois, Eastern Missouri, California, Nevada, Iowa, and Hawaii would be without information on where and when the techtonic menace strikes next!!

So now that all you curious kittens out there know a bit of the score, lets go back in time to the beginnings of our friend...SEISMOLOGY!!!

The History of Seismology

Seismology came into existance about 4 Billion years ago as the Earth began to cool after the Hedean Eon, but we are going on a human level here, folks. In the deep time spectrum, Seismology is an unfertalized egg of an idea.

Back in the olden times, early thinkers attributed earthquakes to the movement of underground animal life. Even Mr. Kool G Philosopher Aristotle took a stab at seismicity, attributing it to underground winds. Nice try, 'Totle. The real kicker for human kind to get a move on with seismology was the 1755 tsunami that killed an odd 70,000 people in Lisbon, Portugal. After this and subsequent devastating earthquakes all around the world, the field of seismology began to grow (the word SEISMOLOGY comes from the Greek word for "earthquake").

Beno Gutenberg

http://www.nap.edu/readingroom/books/biomems/bgutenberg.html

Beno Gutenberg is known for many advances in the field of SEISMOLOGY, but his most well-known achievement was the invention of the RICHTER SCALE. Gutenberg was instrumental in the creation of this scale, with which the power of Earthquakes can be measured by crustal actions, not just population reaction and property destruction (along with his buddy, CHARLES RICHTER, who for some reason got the name). Gutenberg also made giant leaps in the early twentieth century, makeing predictions regarding the differences between continental and oceanic crust. This would later on prove prophetic in the creation of technologies for exploring oceanic crusts and in the later formation of the theory of continental drift. These two Seismic bad boys also penned the four widley accepted Geological papers entitled ON SEISMIC WAVES.

Chuck Richter

http://www.menichella.it/sismolab/ sismo6.html

Aside from these handsome devils, entire institutes have trailblazed seismology throughout history. Seemingly one of the most noted is the California Institute of Technology's "Seismo" Laboratory. Founded in 1921, some of the most important research in seismological studies has been conducted here. The efforts of founder Harry Wood and associates led to the development of one of the most highly used seismographs in history, and is still in use in certain areas today. By 1932, the Caltech Seismo lab had placed multiple seismological instruments all over southern California (it is no secret that this was probably a good idea). Good seismologists are needed for such important scienctific and humanitarian work.

Related Links

Advanced National Seismic System (ANSS)

You can get here straight from the United States Geological Survey Homepage, or just use the direct link. They have great information updated constantly regarding seismic activity all over the world.

Harvard Seismology

I know its cheap, but if you are really into seismology, maybe you can explain some of this stuff to me. Lots of good diagrams, and detailed info for the super-Seismo Geek.

Incorporated Research Institutions for Seismology (IRIS)

Pretty good information and a great earthquake monitor. Just like the ANSS site, but a few differences

In actual books, I used

Stein, Seth, and Wysession, Michael. An Introduction to Seismology, Earthquakes, and Earth Structure. Malden, MA: Blackwell, 2003.

This, ladies and gentlemen, is an ocean bottom seismograph. Its a fancy hunk a metal, isn't it?

www.goin.nasda.go.jp/GOIN/ MRI/htdocs/MRI-PSVR.htm

SEISMOLOGY IN GENERAL:

http://www.passcal.nmt.edu/~bob/passcal/earthquake.htm

Seismology?

For the uninformed, seismology is the study of movements known as SEISMIC WAVES on and under the earth's surface, particularly those caused by earthquakes. Other seismic activity, such as volcanism and human activities such as nuclear weapons testing, are included in seismological study. However, seismologists deal mainly with the tectonic actions that cause earthquakes. According to Stein and Wysession's An Introduction to Seismology, Earthquakes, and Earth Structure, seismological study can be broken down into three concepts: source, medium, and receiver. The source is the movement itself, the medium what the movement is going through (different types of rock, sediment, etc.) and the receiver being the instrument that picks up the waves coming through the medium. Basically, plate tectonics cause movements, geological development dictates what the movement goes through, and human geology nuts pick up the rumblings down in our great planet's deep, hot, and rather fussy bowels.

So why should I care?

Well, most people don't need to care. In the US in 1996, twice as many people were killed playing football than those killed by earthquake activity. It turns out that most of the world is not under substancial seismic threat. If you live in Indiana, like me, there is little chance you would be concerned about the seismic activity in your area. However, if are lucky enough to live in San Francisco or Iran, you would be concerned with the techtonic plate movement that causes most seismic activity. Not from any geological curiosity, but more financial and moral concerns: that is, your house could be leveled or your life could be lost. SO PAY ATTENTION!!!

So what kind a waves we talkin' here?

That's easy. There are a few different types of Seismic Waves:

P-Waves: When an earthquake hits an area, these waves reach far distances first, traveling at speeds of up to 8 kilometers/second. P-Waves are also known as Compressional or Primary waves. As you can see by the illustration, P-Waves move the ground in a forward thrusting motion.

S-Waves: Also known as Shear or Secondary waves. The reason S-Waves cause dangerous earthquake movement is that they move the ground side to side, which explains their slow movement in comparison to P-Waves. Their speed averages 4 km./second

.

Link is too long to put here

Both S and P Waves are known as body waves, that is, waves that move from the Earth's interior. There are two other important types of waves.

Love Waves: These waves hit the surface with a side-to-side movement similar to the S-Wave.

http://www.geo.mtu.edu/UPSeis/waves.html

Rayleigh Waves: Although S-Waves send an initial shock to the surface, these waves are the true killers. Rayleigh waves move the ground up and down and sided to side, resulting in constant opposing movements in the ground. You see pictures of earthquake damage like this and it is a good guess that...

http://www.columbia.edu/itc/seas/E6256/earthquakes/building.gif

...that is a RAYLEIGH, baby. Nasty stuff, huh?

http://www.geo.mtu.edu/UPSeis/waves.html

Hold up a second, buddy. How do seismologists know about these waves, and how can they tell which is which?

For those queries, check out some of that history I have given you. The technical aspects (that is, thousands of mathematical equations) of seismology are pretty dense, but this history will give you some basics. What I can tell you is how they pick up the existing waves going on underneath our feet. Seismologists use instruments called SEISMOGRAPHS to detect underground seismic activity. The first seismographs were just an ink pen and a rolling sheet of paper. The pen is mounted on a spring based mechanism that can pick up the sideways movements of S-Waves and the forward movements of P-Waves. However, these graphs have become somewhat obsolete as the ease of digital technology has come upon us. Now we can measure seismic movement with digital instruments, which require less maintanence and better results.

Link to other Student Webpages for 2004 Earlham Physical Geology

Copyright © 2004 Earlham College. Revised April 15, 2004. Send corrections or comments to parkero@earlham.edu