Science and Computers I -- PHY307/607

Lab 13. - Simulation of Earthquakes

As we discussed in class it is possible to construct a simple simulation for earthquakes using a model in which the material between two tectonic plates is modeled using a set of masses joined together and to the top plate by springs and experiencing a frictional resistance from the lower plate. Earth quakes correspond to motion of one or more of these masses in response to motion of the top plate. The magnitude of the earthquake is the logarithm of the total energy released - large earthquakes correspond to large numbers of masses moving fast or for a long time while small ones correspond to the slipping of just a few masses for a brief time.

The applet which we will use plots the power of the earthquake (the energy released per unit time) on the y-axis against time (on the x-axis). The textbox carries the total energy released during the quake. Initially, and after every earthquake event is drawn the simulation stops - you must restart the simulation each time by pressing Go.

  1. Create a directory called Earthquake under public_html and download the java source codes to this directory. Also, create a file called Earthquake.html which launches the applet (the code will be called Earthquake.class). Set the width and height parameters for the applet to 500 and 250 respectively.
  2. Compile the source and set all appropriate file and directory permissions.
  3. Point Netscape at this applet. Hit Go. After a few seconds you should see the profile of the first quake - disregard this one (it is not typical) and hit Go again. From now on record the total energy released by each quake (don't forget to hit Go each time to start a new quake).
  4. Do this at least 40 times.
  5. Are big quakes more probable than small or vice versa ?
  6. You should see that almost all the earthquakes have total energies E between about 0.1 and 10.0. Divide this interval into 20 regions eg. the first interval ranges from E=0 to E=0.5, the next from E=0.5 to 1.0, the twentieth from E=9.5 to 10.0. Count the number of earthquakes which fall inside each interval.
  7. Plot (using for example Excel) the logarithm of the number of quakes inside an interval against the logarithm of the mean energy in an interval (eg. the first interval would have a mean energy of 0.5*(0.0+0.5)=0.25).
  8. What shape of curve do you see ? If I were to fit the data with a straight line what would be its gradient ?
  9. Does your simulation agree with the Gutenberg-Richter law ?
  10. Edit the file Simulation.java and change the number of masses N from 100 to 50. Recompile and rerun the simulation. Is the biggest quake larger, smaller or equal to the one from the previous simulation ?
To get credit for this lab you need to
  1. Hand in written answers to the questions posed in the lab.
The deadline to get these things to me is next Thursday.
Back to the PHY307 Homepage
This page maintained by Simon Catterall, last updated 29 November, 2001.