The varying intensity grades of an earthquake can be plotted on a map, producing what is called an isoseismal map. Now you will construct such a map, using the following compilation of reports for the earthquake that struck California on April 18, 1906 at 5:12 am. Compare the descriptions provided from each area to the Modified Mercalli scale (upper frame), and assign an intensity to each report. Record this intensity value in the circle next to the abbreviation for the location on the copy of the map that has been distributed to you. By way of example, the first three locations are done for you.

NOTE: The abbreviations following the town- or city-names are those used to designate localities on the map. Plot each intensity value on the map inside the circle next to the abbreviation for the location. You may use the Arabic numerals (i.e., 0, 1, 2, ..., 11, 12) instead of the Roman numerals (0, I, II, ..., XI, XII). Use a contour interval of 2 (II), with contours for 2, 4, 6, 8, etc. It is advisable to start from the high-end, as follows:
 

1. Find your highest even-numbered intensity. Draw a loop enclosing all the places with the highest even-numbered intensity, and any higher odd-numbered intensities.
 

EXAMPLE: If your highest even-numbered intensity is 10, then the loop should enclose all the 10's and 11's. All intensities lower than 10 should be outside of the loop.

2. Now draw a loop enclosing the places of the next lower even-numbered intensity.
 

In the EXAMPLE, the next lower even-numbered intensity is 8. Draw a loop to enclose all the 8's (and 9's). All intensities lower than 8 should be outside the loop.

3. And so on, down to the loop enclosing all the 2's (and 3's), and excluding all intensities less than 2. Stop here.

When your isoseismal map is completed, you will be able to determine the approximate location of the epicenter. Mark the epicenter with a star on the map.