Download Virtual Earthquake Name Date Objective: To use an on

Virtual Earthquake
Name
Date
Objective: To use an on-line program to learn how seismologists use data from seismograms to
determine earthquake epicenter locations and calculate the Richter magnitude of earthquakes.
1. Log onto the computer and open a web browser.
2. Go to my website: www.lsrhs.net/sites/singlerc Under ES1 Links, Volcanoes &
Earthquakes sites, select “Virtual Earthquake”.
3. Scroll down the screen. Click on the box that says “Execute Virtual Earthquake”.
4. Read “What’s an Earthquake?” and “What are Earthquake (Seismic) Waves?” P waves
travel through
; S waves travel through
Average speeds of P waves:
Average speeds of S waves:
5. What’s a Seismogram? Study the graph and read the text in this section. Your ability to
accurately read a seismogram is critical to your success in this activity.
6. LABEL the parts of the seismogram on the picture below.
7. Match the following terms with their descriptions. (Figure it out from the graph.)
S wave arrival time
a. where the graph first goes up or down relative to “0”
P wave arrival time
b. y-axis (amplitude) units
S – P interval
c. the height of a wave from the center line on the graph
Amplitude
d. x-axis (time) units
millimeters
e. difference in time between arrival of P and S waves
seconds
f. the second time the line goes up and down a lot
8. How is an Earthquake’s Epicenter Located? Seismograms from at least
stations are
needed to locate an earthquake’s epicenter. The
from each
seismogram is used to determine the distance the waves traveled from the origin of the
earthquake to that station. The actual epicenter is on the
of a circle
drawn around a station, where the circle’s radius equals the
. One
station will tell only distance to epicenter, not
. With data from a minimum
of three stations, seismologists can
the epicenter location.
9. Let’s have an Earthquake! Select one of the four regions listed. Circle the region you
selected: San Francisco area Southern California Japan region Mexico
Click “Submit Choice”.
10. Scroll down below the map. You will again see the sample seismogram. Read “Measuring
the S-P Interval”. Note that the seismogram scale is set so the P-Wave arrival time equals 0
seconds. To determine the S-Wave arrival time, look for the first major peak above OR
below the 0 line. This seismogram shows an S-P interval of 36 seconds. If you do not
understand how this number was determined, ASK NOW!
11. Click on “View Seismograms”.
12. Here are three seismograms from an actual earthquake that occurred in the region you
selected. Determine the S-P interval for each seismogram. Type the times in the spaces on
the screen AND record data in the table below. Notice that the scale may be different on
different seismograms.
Station Name
S – P Interval (seconds)
13. Click “Convert S-P Interval”. Read “Determining the Earthquake Distance”. The graph
shows curves for P wave and S wave arrival times versus distance, and a third curve for S-P
interval versus distance. You will use the line labeled “S-P”.
For example, according to the graph, at a distance of 200
km, the S-P interval is
seconds. At 640 km, the
S-P interval is
seconds. As the distance from the
epicenter increases, the S-P interval
.
14. Scroll down to “Determining distance from S-P”. Use the
graph and the times you recorded in the last step to
determine the distance to the epicenter for each seismograph
station. Notice that the times you previously selected are
already on the chart. Now carefully read the S-P curve to
find the distance. Type the distances in the spaces on the
screen AND record data in the table below. Accuracy is
extremely important in this step or you will have to do it
again later.
Station
Epicentral Distance (km)
1
2
3
15. Click “Find Epicenter”. View the map on the screen. The epicenter is the place where the
three colored circles intersect. How close did you get to the actual epicenter?
If you get “very close” or “oops” go back and try again. “Oops” probably means you made a
mistake reading the original seismograms; “very close” probably results from a mistake
reading the S-P graph. Correct your work and try to get an “Excellent” rating. If you go
back and make corrections, be sure to correct the data in the tables in Steps 13 and 15.
If after two attempts you are unable to get a close reading, click “View True Epicenter”.
Compare the two maps and the data. Describe where you went wrong:
16. Study the map of the epicenter location. Describe the geographic location of the epicenter.
17. Read “More about epicenter being an exact point.” Why should you NOT expect an exact
point when you locate the epicenter? What factors can influence your data?
18. Click “Compute Richter Magnitude”. Read “Magnitude Explained”.
19. What are some ways that the relative strength of an earthquake can be evaluated?
20. Richter magnitude compares earthquake strengths based on
. What is the lowest Richter magnitude that is strong enough for people to feel?
21. Scroll down to the graph. The two measurements needed to determine Richter magnitude are
and
. Be
careful of the scale when reading the graph. The highest S wave amplitude on the sample
seismogram is
mm.
22. Click “Go to Next Page”. Read “The Richter Nomogram”.
The Richter scale is exponential, meaning that a change in 1 unit of Richter magnitude
increases the maximum amplitude by a factor of
. The magnitude is determined on
the nomogram from the place where data from three or more seismograms intersect. The
sample nomogram shows a magnitude of
.
23. Click “Go to Next Page”. You will again see the three seismograms, but now you will read
the maximum S wave amplitude for each station. Check the peaks above AND below the 0
line to find the maximum amplitude. Be careful to check the scale for each seismogram.
Type the amplitudes in the spaces on the screen and record data in the table below.
Station
1
2
3
Maximum S Wave Amplitude (mm)
24. Click “Submit to Nomogram”. You should have three lines that intersect at a single point on
the Richter scale. If they do not intersect, go back and recalculate the amplitudes. Record
the estimated Richter magnitude:
.
25. Click “Confirm Magnitude”. What was the actual magnitude of the earthquake?
Where and when did the actual earthquake occur?
26. When you are finished, you may print a certificate if you choose. Enter the information
required. Click Get Certificate and print your final data summary table and certificate. To
print, go to “File – Page Set Up”. Choose horizontal orientation and reduce to 85%. Print to
the Science Lab printer.
27. Go to the following web site: http://earthquake.usgs.gov -- you will see a map under the
heading “Latest Earthquakes”. Click on the map.
Use the tool in the upper right corner of the map to zoom out until you can see a world map.
Note the legend at the bottom of the screen. How do you distinguish whether an earthquake
occurred in the last hour, day or week?
Different sized dots distinguish different magnitudes. The list on the left indicates
magnitude, location, time and depth of earthquakes for the last day.
Find the largest magnitude earthquake shown on the map – move the cursor over the dots to
see the magnitude values. Click on the highest magnitude location; this will highlight the
information about that earthquake in the data table. Where (location) did it occur?
When (date & time) did it occur?
What
was its magnitude?
What was its depth?
Use the tool in the upper right corner to “zoom to” the United States then use the “+” sign to
zoom in enough to see state outlines. Name all states in the 48 contiguous states where
earthquakes have occurred in the last week. (NAMES not abbreviations)
Click on the dots to see information about the quakes. When and
where was the largest one?
What was its magnitude and depth?
Now “zoom to” Alaska. Where in Alaska do most earthquakes occur?
Zoom to Hawaii. Where in Hawaii do most earthquakes occur?
Return to the original page (earthquake.usgs.gov) and scroll down to the bottom of the page
and click “Top 10 Lists and Maps”. Under “World”, select “Deadliest Earthquake each Year
since 1990”. The left side lists “Largest Earthquakes”; the right side lists “Deadliest
Earthquakes”. Is the largest quake each year also the deadliest?
Compare the largest and deadliest earthquakes for each of the years listed below. If the
largest earthquake was also the deadliest one, indicate the location, magnitude and number of
fatalities. If the largest was not the deadliest, then give the location, magnitude and number
of fatalities for BOTH the largest and the deadliest earthquakes that year.
2012
2011
2010
2008
2004
Give at least two reasons why the largest earthquake in a year may NOT be the deadliest.