Click2Disasters - The San Francisco Earthquake: A Pictorial History, Inside the Earth - Chapter 2

<body link="0000ff" alink="ff0000" vlink="000000" bgcolor=000033> <table width="100%" bgcolor=000033> <tr> <td align=center valign=top> <table width=90% bgcolor=ffffff> <tr> <td align=center valign=top> <tr> <td> <div align=center><p><b><font face="arial, helvetica" size=5 color=000000><b>SAN FRANCISCO EARTHQUAKE</p> <p><font size="4">CHAPTER 2 - INSIDE THE EARTH</b></font></p> </div>  <center> <table width="90%"> <tr> <td align="left" valign="top"> <div align="justify"> <p><font face="arial, helvetica" color="000000" size="3">Before we can understand the natural disaster that befell the citizens of San Francisco, in 1906, we need to know something about the Earth's composition. How is it constructed? Are earthquakes, like the one which decimated the city, predictable? The answers, and the information currently known about earthquakes, may surprise you.</p> <p>What would we see if we could look <a href="http://scign.jpl.nasa.gov/learn/plate1.htm" target="_blank"><b>inside</b></a> the earth? Although no one has ever descended lower than the earth’s <a href="http://www.ac.wwu.edu/~debari/406/figs/earth.jpeg" target="_blank"><b>crust</b></a>, scientists have a good idea how the planet’s interior is configured.</p> <p>The crust averages 5-40 kilometers in depth. In addition to <a href="http://www.windows.ucar.edu/tour/link=/earth/geology/crust_elements.html" target="_blank"><b>elements</b></a> necessary to sustain life, it is mostly composed of <a href="http://www.science.uwaterloo.ca/~cchieh/cact/applychem/alsilicate.html" target="_blank"><b>alumino-silicates</b></a> with feldspar (<a href="images/green.jpg" target="_blank"><b>green</b></a>) and <a href="http://mineral.galleries.com/minerals/silicate/quartz/quartz.htm" target="_blank"><b>quartz</b></a> (<a href="images/gray.jpg" target="_blank"><b>gray</b></a>) the two <a href="http://jersey.uoregon.edu/~mstrick/AskGeoMan/geoQuerry70.html" target="_blank"><b>most common</b></a> minerals. On the crust’s surface, sedimentary rocks form a kind of thin veneer, but igneous rocks constitute the bulk (about 95%) of the <a href="http://quake.wr.usgs.gov/research/structure/CrustalStructure/database/index.html" target="_blank"><b>total</b></a> crust.</p> <p>Earth’s largest layer - the mantle - is composed of hot, dense rock. Temperatures in this 1800-mile layer get progressively <a href="http://www.npaci.edu/enVision/v14.2/tackley.html" target="_blank"><b>hotter</b></a> (from about 1600 degrees Fahrenheit at the top to around 4000 degrees Fahrenheit at the bottom) while pressures <a href="http://pubs.usgs.gov/gip/dynamic/inside.html" target="_blank"><b>increase</b></a> commensurately (since earth’s temperatures and pressures increase with <a href="http://earth.leeds.ac.uk/dynamicearth/melt/melt5.htm" target="_blank"><b>depth</b></a>).</p> <p>Because of the mantle’s temperature <a href="http://volcano.und.edu/vwdocs/vwlessons/lessons/Earths_layers/Earths_layers6.html" target="_blank"><b>differences</b></a>, its molten rock <a href="images/flows.jpg" target="_blank"><b>flows</b></a> (just like thick soup which <a href="images/boils.jpg" target="_blank"><b>boils</b></a> in a saucepan) with the <a href="images/consistency.gif" target="_blank"><b>consistency</b></a> of asphalt.</p> <p>Whatever is resting on the flowing molten rock will <i>also</i> move.</p> </div> <p align="center"><font size="2"><a href="san_francisco_ch1.htm">GO TO LAST CHAPTER</a>   <a href="san_francisco_ch3.htm">GO TO NEXT CHAPTER</a></p><br> </td> </tr> </table>  </td> </tr> </table>  </td> </tr> </table> </body>