Introduction to Earth Sciences I
Topic 4
Earthquakes, Seismic Waves, and the Earth's Interior
Objectives:
Earthquakes are one of the most profound expressions of the Earth's dynamics. They provide the most direct evidence that the rigid outer shell of the Earth is in motion. They are also the cause of huge tragedy as seen in earthquake losses in the last two years (see Case Studies below). The objective of this part of the course is to provide some basic information on earthquakes as physical phenomena, what makes them happen and why they happen where they do, and how the propagation of seismic energy generated by earthquakes propagates through the Earth and can be used to infer information about the interior properties of the planet. So I hope you will come away from this course having a basic understanding of -
1. What an earthquake is, why they occur, and why they occur where they do.
2. How the seismic waves generated by earthquakes are used to image the Earth's interior and some things we have learned from these images.
Your text is reasonably good on the basics of this subject (Chapters 14 and 15) but neither of the book's author's are seismologists and you can find better treatments of most of the material at Web sites created by researchers at earthquake research centers. The four that I think will be most useful are:
http://vearthquake.calstatela.edu/ which is from Cal State LA and goes through a number of simple exercises in finding earthquake locations etc that we will do in class or in the lab.
http://scecdc.scec.org/eqcountry.html and http://www.scecdc.scec.org/Module/TableofC.html from the Southern California Earthquake Center, a consortium of universities in Southern California (but including Columbia) who combine to do research on earthquakes and their associated hazards. I have had the most difficulty getting to this site. We will use quite a lot of materials from this site.
We will discuss two new discoveries about the deep earth that
seismic analysis has revealed. One is the "super-rotation" of the
inner core. A description of that can be found at
http://www.ldeo.columbia.edu/press_releases/song/pr.html which includes
an animation. The scientific paper is published in the journal Nature
and would be too technical for our purposes.
We will also study the nature of the so-called D'' Layer which is at the boundary between the outer core and the lower mantle. It exhibits a surprising degree of heterogeneity and structure suggesting that the core/mantle boundary is a very dynamic interface. This was published in Scientific American in May 1993 by Jeanloz and Lay. It's a very accessible article that you should be able to read without much difficulty.