LabWorksheet10_PlateTectonics&Earthquakes-1
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Feb 20, 2024
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Lab Worksheet 10: Plate Tectonics and Earthquakes
GEOG 5, Instructor: Joy Fritschle
In this lab, you will explore landforms created by tectonic boundaries and mass movement, and investigate earthquake activity and risk. In part 1 of the lab, you will explore tectonic plates and their associated landforms. Part 2 will allow you to gain a better understanding of earthquake magnitude and energy. Part 3 will entail an exploration of earthquake activity and risk for a study site in California. Part 1: Plate Tectonics and Associated Landforms
.
1.
On the figure below label the main tectonic plates. You can use the Living Atlas GIS data from the previous
lab to help you (
Tectonic Plates and Boundaries
, direct link: https://arcg.is/49muz). Please note that this is not a complete list of all tectonic plates. (
3.5 pts)
• Pacific Plate
• Caribbean Plate
• Nazca Plate
• Eurasian Plate
• North American Plate
• Arabian Plate
• Antarctic Plate
• African Plate
• Cocos Plate
• South American Plate
• Australian-Indian Plate
• Juan de Fuca Plate
• Philippine Plate
2.
Where are you located, and on what plate are you located on? (0.5pts)
3.
Along much of the California coast, is the oceanic Pacific Plate converging, diverging, or sliding past in relation to the North American plate? What is the approximate length of this plate boundary in California? (use the scale provided or go to the map online at https://arcg.is/01nLzS0
and use the measurement tool to estimate its length) Note: this boundary represents the San Andreas Fault Complex. (0.5pts)
___________________ 4.
What type of tectonic plate boundary is found in the Gulf of California? Do you think that Baja was once attached to mainland Mexico? Why or why not? (0.5pts)
5.
Using the map on the previous page, identify the type of plate boundary (convergent, divergent, or transform) at the following locations. Use Google maps to help
locate these landforms. (2pts)
Aleutian Trench (on the ocean floor south of Alaska): .
Himalayas (folded/faulted mountains) on the north edge of Indian
sub-continent: .
__
Peru-Chile Trench and the Andes along the west coast of South
America: .
Mid-ocean ridge across Iceland: .
Ryukyu Island Arc in Southeast Asia: .
_
Mariana Trench in the western Pacific Ocean, to the east of the Mariana Islands: .
East Africa Rift Valley: .
_______
San Andreas Fault: .
Part 2: Earthquake Magnitude and Energy
In this part of the lab, you will gain a better understanding of the measurements we use to study earthquake magnitude and energy. The Richter scale is used for determining the magnitude of an earthquake. The Richter scale is logarithmic so each time the magnitude increases by 1.0 there is a ten-fold increase in the measured amplitude. In terms of the energy released by an earthquake, each number increase on the Richter scale represents approximately 32 times more energy released. Typically, seismologists no longer use the Richter scale except for local earthquakes (within about 150 kilometers) that are smaller than 4.0 on the scale. The Richter scale was developed in the 1930s and there are now more sophisticated ways to determine an earthquake’s magnitude.
For earthquakes larger than 4.0, the Moment Magnitude scale (M
W
) is used. Like the Richter scale, it is logarithmic. The Moment Magnitude scale was designed so it is roughly equal to the Richter scale (for example,
a 6.5 earthquake on the Moment Magnitude scale is roughly equal in magnitude to a 6.5 earthquake on the Richter scale). The Moment Magnitude scale is calculated based on the distance the fault moved (its slip), the strength of the rocks along the fault (the rock’s rigidity), and the area of the fault that slipped. 6.
To give you an idea of how much more energy is released by earthquakes of different magnitudes you will use an online calculator from the United States Geological Survey: “How Much Bigger…?” Calculator
website (direct link: https://earthquake.usgs.gov/education/calculator.php). (1 pt)
A magnitude 6.0 earthquake is _________ times bigger than a magnitude 5.0 earthquake, but it is ________ times stronger (energy release). A magnitude 7.0 earthquake is _________ times bigger than a magnitude 5.0 earthquake, but it is ________ times stronger (energy release). A magnitude 8.0 earthquake is _________ times bigger than a magnitude 5.0 earthquake, but it is ________ times stronger (energy release). A magnitude 9.0 earthquake is _________ times bigger than a magnitude 5.0 earthquake, but it is ________ times stronger (energy release).
The table on the next page provides the number of earthquakes that occurred at different magnitude ranges above 5.0 M
w
from 2000 to 2019. By comparison: ➢
approximately 1,000,000 earthquakes with a magnitude of 2.0-2.9 occur each year,
➢
approximately 100,000 earthquakes with magnitudes of 3.0-3.9 occur each year, and
➢
approximately 10,000 earthquakes with magnitudes of 4.0-4.9 occur each year.
The number of earthquakes with magnitudes of 7.0 and greater has remained relatively consistent since recordkeeping began. Although the average number of large earthquakes per year is fairly constant, they can occur in clusters. However, that does not imply that earthquakes that are distant in location, but close in time,
are related. There has definitely been an increase in the number of earthquakes that have been detected and located due to a more than 10-fold increase in the number of seismic stations worldwide over the past century.
Use the table on the next page to answer the following questions. 7.
In what year did the highest number of 8.0+ magnitude earthquakes occur? Is this the same year that the highest number of 5-5.9, 6-6.9, and 7-7.9 earthquakes occurred? (0.5pts)
8.
On average, how many 8.0+ magnitude earthquakes occurred between 2000 and 2019? (Add the number of earthquakes in the 8.0+ M
W
column and divide that number by twenty.) (0.5pts)
On average, how many 7-7.9 magnitude earthquakes occurred between 2000 and 2019? (0.5pts)
9.
Suppose a friend asks you, “Why are we having so many more earthquakes this year?” Explain your response in one to two sentences. (1 pt)
Worldwide Earthquakes, 2000-2019
Year
5-5.9 M
w
Count
6-6.9 M
w
Count
7-7.9 M
w
Count
8.0+ M
w
Count
2000
1,344
146
14
1
2001
1,224
121
15
1
2002
1,201
127
13
0
2003
1,203
140
14
1
2004
1,515
141
14
2
2005
1,693
140
10
1
2006
1,712
142
9
2
2007
2,074
178
14
4
2008
1,768
168
12
0
2009
1,896
144
16
1
2010
2,209
150
23
1
2011
2,276
185
19
1
2012
1,401
108
12
2
2013
1,453
123
17
2
2014
1,574
143
11
1
2015
1,419
127
18
1
2016
1,550
130
16
0
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