Instructions:
Complete the following exercise on the attached pdfThere are two parts to this homework:Part 1: Magnitude, Frequency and Position of Major Earthquakes on EarthUse the tables and maps provided in the PDF to help you answer the questions. Part 2: The USGS Real-Time Live Earthquake MapUse the map and website link (https://earthquake.usgs.gov/ (Links to an external site.)) in the PDF to help you answer the questions. Homework #2
Name _______________________
Global Earthquake Occurrence Activity
Learning Objective:
•
•
Describe the evidence used to estimate the timing of giant earthquakes on subduction
zones, especially the Cascadia subduction zone
Explain how frequency of earthquake occurrences varies with earthquake size
Instructions:
1. View the video: Latitude and Longitude Video.
2. Complete the following exercise.
Part 1: Magnitude, Frequency and Position of Major Earthquakes
on Earth
Let’s look at the earthquake records for magnitude 5.0 or larger events that have occurred over
the past decade (2009 – 2019). You can find the results in the table below. Use this table to
answer Questions 1-5, and reflect on how the frequency of earthquakes across various magnitude
ranges.
Number of Earthquakes Worldwide from 2009 – 2019
Magnitude
ranging
between
2009
2010
2011
2012
2013
2014
2015
2016
8.0-9.9
1
1
1
2
2
1
1
0
2017
1
2018
1
2019
1
7.0-7.9
16
21
19
15
17
11
18
17
7
16
9
6.0-6.9
144
151
204
129
125
140
124
128
106
117
133
5.0-5.9
1,896
1,963
2,271
1,412
1,402
1,475
1,413
1,502
1,451
1,675
1,,489
Total
2,057
2,136
2,495
1,558
1,545
1,627
1,556
1,647
1,565
1,809
1,632
Source: USGS
Study the chart above, and then answer the following questions:
1. On average, how many earthquakes happen per year in the 8.0 – 9.9 magnitude range?
2. On average, how many more earthquakes in the magnitude range of 7.0 -7.9 occur,
compared to those in the 8.0 – 9.9 magnitude range?
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3. On average, how many more earthquakes in the magnitude range of 6.0 -6.9 occur,
compared to those in the 8.0 – 9.9 magnitude range?
4. On average, how many more earthquakes in the magnitude range of 5.0 -5.9 occur,
compared to those in the 8.0 – 9.9 magnitude range?
5. What year had the highest frequency of large (M8.0+) earthquakes?
Now, we are going to look at a table that compares death toll with earthquake magnitude from
the events of 2019. Note, these are just the magnitude 7 and larger events. Data compiled by
USGS.
6. The largest magnitude earthquake in 2019 resulted in how many deaths? _____________
7. Of the 10 earthquakes listed above, how many resulted in human deaths? _____________
8. Are earthquake magnitude and death toll strongly correlated? (Meaning, does the
increase in magnitude always correspond to an increase in death toll)? ____________
Speculate as to why? ______________________________________________________
________________________________________________________________________
9. How deep was the shallowest earthquake, magnitude 7 or higher, in 2019? (The depth
listed is where the origin of the earthquake, the hypocenter, occurred). ________________
10. How deep was the deepest earthquake, magnitude 7 or larger, in 2019? _____________
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The next step will revisit the idea of earthquake depth versus type of plate boundary.
Earthquake
Peru
Indonesia
Magnitude Depth (km) Latitude Longitude
7.0
267.0
-14.71
-70.16
7.3
212.0
-6.41
129.16
Using the latitudes and longitudes given above, plot these two deepest earthquakes on
Map A on page 4. If you don’t know what latitude and longitude are, please see the Latitude and
Longitude Video.
Then take those locations and plot them on Map B on page 5. Use the map legend to help you
answer question 11.
If you don’t have a printer, you can save each map as an image to your computer. Then
open Power Point and use the symbols tool to plot a circle at these latitudes and
longitudes. Use your observations to answer Question 11 below.
11. Now reflect on our discussions of the relationship between earthquake depth and plate
boundary type. Along what kind of plate boundary did the two deepest earthquakes in
2019 occur?
*Why? What is it about this kind of boundary allows for deep earthquakes to occur?
*Remember that earthquakes only occur in the lithosphere. But at the plate boundary type you
listed above, lithosphere descends into the asthenosphere. As it descends, it retains its brittleness
and rigidity, and thus earthquakes occur in the descending slab of lithosphere.
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Map A
4
Map B
5
PART II: The USGS real-time Earthquake Map
Use an internet browser and type in this link (https://earthquake.usgs.gov/) Earthquake.USGS
Click on the Latest Earthquakes interactive map to open the real-time earthquake display. The
first thing that should pop up is a gray map of the United States, with some red lines by the west
coast. The red lines represent plate tectonic boundaries. There might be a few colored dots that
represent earthquakes. Here is an example of what the Western US looked like, with some
earthquakes included, at the time I made this homework.
12. Note the letters labeled on the
tectonic plates to the left. Choose the
correct tectonic plate for each letter:
(We have now discussed these plates
several times).
12a) Plate A is ____________________
12b) Plate B is ____________________
12c) Plate C is ____________________
12d) Plate D is ____________________
Now, click on the gear icon in the upper right part of the screen (the settings button). Change the
setting to “7 Days, Magnitude 2.5+ US”. Many colored circles should pop up. You can zoom in
and out to view different regions of the world using the “World icon” or the +/- in the upper left
of the map. In the upper right of the map, there is a “Basemap & Overlay” icon and “Legend”
icon that allow you to access more details about this map.
13. What do the locations of the circles represent? ___________________________________
14. What do the colors of the circles represent? _____________________________________
15. What does the size of the circles represent? _____________________________________
16. Do all earthquakes in the United States occur along plate boundaries? ______________
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17. Provide an example of a location where earthquakes occur in an area away from a plate
boundary. ___________________________________
18. What state (of the lower 48) appears to be the LEAST seismically active? Select your
answer from the options (a-d) below:
a)
b)
c)
d)
Maine
Oklahoma
California
Nevada
On your map, open the menu for the “Basemaps & Overlay” icon and select click “Satellite”
(you were previously in Grayscale). Now, zoom in to the junction between the Pacific, North
American and Gorda plates (the triple junction!).
19. After looking at the shapes and colors on the satellite image, what is happening in the
region where the Pacific, Gorda and North American plates meet? (Hint: think about what
the map is showing you at that junction.) Select your answer from the options (a-d) below:
a)
b)
c)
d)
A collision producing mountains that are 3 km above sea level
A sag pond or releasing bend in the San Andreas fault
The ocean depth changes dramatically
The coastline matches the plate boundary perfectly
Now, change to the “Street” Basemap & Overlay option and select the box that says “U.S.
Faults.” What you have done is turned on a layer that contains all the major mapped faults in the
U.S. (Pretty neat, huh!). Zoom in to northern California so you can see the name “Eureka” on
your map
20. Are there identified faults in the region around Eureka and Humboldt Bay?
__________
21. Do these faults all align with the same orientation? ____________________________
Now zoom out and locate Ukiah, CA on the map (it is in Mendocino County along the Hwy 101
corridor).
22. Is there a fault running through the town of Ukiah? ____________________________
23. It runs parallel to a well-known fault. Can you name the well-known fault? Provide the
name (Spelling counts!) __________________________________________________
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Now zoom out and locate the region near Santiago, Chile in South America. Go back to the gear
icon in the upper right part of the screen (the settings button). Change the setting to “30 Days,
Magnitude 2.5+ US”. Many colored circles should pop up.
24. What do you observe about the trend of earthquake activity in this region?
______________________________________________________________________________
______________________________________________________________________________
25. Using your computer, take a screen capture of the earthquakes. Upload this image and
label it #25
26. What kind of plate boundary do we see in this region? _____________________________
27. On August 31, 2020 a magnitude (M) 6.8 earthquake occurred in this region near the
community of Vallenar. Use this map to zoom in and determine the depth of this earthquake.
(Record your answer in km) (Hint: If you click on the circles, a detail box opens in the lower
left of your screen.) _________________________________________________
28. Is this a shallow, intermediate or deep earthquake? _______________________________
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