Earthquakes: Epicenter determination, magnitude and seismic waves
In this part of the lab you will be interacting with a web site to calculate the magnitude of an earthquake and it’s location. Read the web site carefully as you go and answer the questions as you work your way through this lab. You may want to use your book as a reference, so have it nearby. When you finish with the epicenter/magnitude determination there is a certificate that you MUST print out and attach to your lab when you turn it in on. If you don’t do this you won’t get credit!
WEBSITE: http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.html (this site can be found on the class web page if you have problems linking to it)
Log on the web site above and answer the following questions:
1) What causes an earthquake?
2) What is the focus of an earthquake?
3) What do seismic waves transport?
4) What are the two types of earthquake waves discussed on this web site and how are they different from each other?
5) Which of the two types of earthquake waves discussed is the fastest?
6) What is a seismogram and what does it show?
7) How would a true seismogram look compared to the simplified version used in this exercise? Why would it look different? (to see some actual seismograms go to: http://www.geol.binghamton.edu/seismogram.html)
8) What is the epicenter of an earthquake? (what does it represent?)
9) How many different locations of seismic stations are required to determine the epicenter of an earthquake?
10) Why are this many locations needed?
For the next part of the lab you will find the epicenter and magnitude of one of the earthquakes listed. Work your way through the next few pages carefully and be sure to follow the directions on the web page. When you finish be sure to print out your certificate to turn in with this assignment.
Which earthquake are you going to calculate the epicenter and magnitude for? ____________________________________
In order to calculate where an earthquake epicenter is you must calculate the difference in time from the arrival of the p-wave and the s-wave. This is known as the s-p interval and it can be used to determine the distance a quake is from the station.
Look at the sample seismograph below the map of the area you have chosen.
11) Which wave type arrived first at the station?
12) For each vertical line on the graph, how much time is represented?
Click on View Seismographs
For each of the three seismographs on the web site write the name of the station and the s-p time
Station Name Travel Time (s-p time)
1)
2)
3)
Click on Convert s-p interval
You are now going to use a graph known as a time/distance travel graph to calculate distances. Because earthquake waves are, for the most part, predictable in their velocity we can use the s-p values above to come up with distances
13) What does the y-axis (vertical axis) of the s/p travel graph represent?
14) What does the x-axis (horizontal axis) of the s/p travel graph represent?
15) How can the s-p travel graph be used to calculate distance?
16) Use the practice graph provided and answer the following questions
a) how long does it take the p-wave to travel 300km? _______________
b) How far will the s-wave travel in 40 seconds? _____________
c) What does the s-p line show on the graph?
For each of your stations record how far they are from the epicenter using the s-p curve provided and fill in the table below.
Station s-p Interval (time) Distance
1)
2)
3)
Click on Find the Epicenter
17) How well did you do?
18) How do you know where the epicenter is? What method is used to unite all the data?
Click on View True Epicenter and complete the following table. NOTE: Sometimes this option won’t come up if you did something VERY right or something VERY wrong.
Station s-p interval distance s-p interval distance
1)
2)
3)
19) Where was the epicenter for your earthquake?
20) What is one factor that can affect the speed of earthquake waves? Can you think of another?
Click on Compute Magnitude
21) What does the magnitude of an earthquake measure?
22) What is the Richter magnitude of an earthquake based on?
23) What two measurements are used from the seismogram to calculate magnitude?
24) What is the amplitude of a wave? (draw a picture if it’s easier)
Click on Go To Next Page
25) What is a nomogram?
26) If a station was 100km from the epicenter and the amplitude of the s-wave was 1, what would the magnitude of the quake be?
Click on Go to the Next Page
Measure the amplitudes of the s-waves from the seismograms and fill in the information in the table below.
Station Amplitude Distance
1)
2)
3)
Click on Submit Nomogram
27) What is your estimate for the quake Magnitude?
Click on Confirm Magnitude
28) How well did you do?
29) What was the actual magnitude of the quake and what was it’s name?
Be sure to print the completion certificate and turn it in with this assignment.