Name:
In-class homework for Ch 11 Earthquakes (Part 2, extra credit for a high score)
1) Use the 3 seismograms from Eureka, California, from Elko, Nevada,
and from Las Vegas, Nevada, to fill in the table. Use the last diagram to
relate the S-P travel time difference to the distance from the epicenter.
2) On the map below, use a compass to draw a circle around each seismograph
station. The radius of each circle should be equal to the distance from the
epicenter you found above. Use the map scale to measure the radius of the circle.
Find a map of the western United States and identify the location of the nearest
town to the
earthquake
epicenter.
The nearest town to the epicenter is
.
2
3) To calculate the magnitude of an earthquake you
need the S–P time interval and the maximum amplitude
of the seismic waves. Confidence in your magnitude
estimate increases if you do this for multiple
seismograph stations. From the seismograms on the
previous page, measure the maximum displacement
(amplitude) of the S wave (use the vertical axis and
measure from 0 in one direction). Fill in the table to the
right.
4) Use the numbers in your table above and the scales to the right to
calculate the earthquake magnitude. First, plot the station distances on
the far left scale, and the S-wave amplitudes on the far right scale. Then
draw lines connecting each pair of points. Where each line intersects the
middle scale, indicates the estimated magnitude. Write the magnitude for
each station below.
5) Average the magnitudes computed from the three stations to estimate
of the magnitude of the earthquake.
6) Using the location of the epicenter, look up the history of this actual
event on the Web.
What is the name of this earthquake?
When did it occur?
How close is your estimate to magnitude given on the web?