Lab-Earthquakes-GoogleEarth-Fall2021-Online
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Earthquakes (A Google Earth Exercise)
GEL 111 – Geology
Wake Technical Community College Instructor: Ian C. Brown
Name:
Introduction
Seismology deals primarily with the study of earthquakes and seismic waves. Earthquakes are associated with large fractures or faults in the outer layers of the Earth. The focus
(or hypocenter) of an earthquake is the site of initial slip on the fault (below ground). The epicenter
is the point on Earth’s surface immediately above the focus (Figure 1). Figure 1
Two general categories of earthquake or seismic waves are generated by slip (movement) along a fault. Body waves
carry earthquake energy away from the focus in all directions through Earth’s interior. These types of waves have given scientists the most information about earthquakes. Surface waves
, on the other hand, are the concentric ripples of energy that spread out away from the epicenter along Earth’s surface that have been generated from the body waves.
P-(Primary) waves
travel most quickly through Earth’s interior and can travel through any material whether solid, liquid, or gas. Alternatively, S-(Shear) waves
(also called secondary waves) move more slowly and can only pass through solids. Surface waves
travel only along the Earth’s surface and are called Long Waves or L-waves because they
have a long wave period, which is the time required for successive wave crests to pass a fixed reference point. Surface waves are important to planners and engineers because they cause most of the vibrations that cause the most damage.
Recording Earthquake Waves The instruments that scientists use to record and monitor earthquakes are called seismographs
. The vibrations generated by earthquakes and explosions provide the most important means of locating and determining the severity of a quake. Seismographs have been set up at stations all around the globe on all continents. Three sets of waves are seen to arrive at the stations: P waves arrive first, S waves arrive next and Surface waves are last. 1
Figure 2 shows a typical seismogram indicating the arrival of the P and S waves. On a seismogram, time advances from left to right. This recording is measured in minutes. The
recordings may also be measured in seconds (it depends on the scale that is being used).
Figure 2
The vertical axis is ground Displacement, or amplitude (usually measured in millimeters).
When there is no earthquake reading there is just a straight line with small wiggles caused by local disturbances such as trucks passing on the highway.
For this lab activity, you will be working with three separate earthquake events on different continents. You will be using Google Earth Pro to locate the seismic stations, plot earthquake data, and locate the epicenters of earthquakes.
Finding, Saving, and Renaming Seismic Station Locations
You will be given the location coordinates (latitude and longitude) for all the seismic stations. To create the locations of seismic stations in Google Earth, do the following;
(a)
Click the “Add Placemark” tool in the menu bar at the top (the yellow pin icon).
(b)
In the Name field, type the 3 or 4-letter code for the station, eg. KDK.
(c)
Beside the Name field on the right, there is a button showing the yellow pin. Click on it to reveal other options for icons. Select the icon showing three concentric circles. [
]
(d)
Click inside the box beside “Color” at the top of the window. You will see options for changing the color of the concentric circles. Choose a yellow color, then click “OK” twice.
(e)
Type the seismic station coordinates to the latitude and longitude field using only numbers, spaces, and letters. (f)
Click “OK”. The seismic station location is now saved.
Repeat this procedure to the save the locations of all the seismic stations.
Plotting Circles to Locate the Epicenter
To locate the epicenter of an earthquake, we need the distance to the earthquake from three
recording stations. The distance is used to plot a circle around each station, with the radius of the circle representing the distance from that station to the earthquake.
To plot a circle, do the following;
(a)
Select the “Ruler” tool from the Menu and then choose the “Circle” tab. Make sure that your measurement units are set to Kilometers. 2
(b)
Place the measuring box (with the crosshairs) over the station icon, making sure that the station icon is centered in the measuring box. Click once on the station icon and move the mouse or slide over the touch pad to draw a circle with the desired radius. (NB. You may not get the exact distance measurement,
but it should be as close as possible to reduce errors). Once the desired radius is achieved, click once to stop measuring. (c)
In the Ruler dialog box, click “Save” and enter a name to identify the circle, eg. “KDK Circle”. Figure 3. Circles identifying the location of the epicenter.
To determine the exact coordinates of the epicenter, do the following;
(a)
Click the “Add Placemark” Icon on the Menu. The placemark window opens and a flashing icon appears in the main view. In the placemark window, click on the icon to the right of the “Name” field to change it to the red circle with a wave (see below) and click ok.
[ ].
(b)
With the epicenter icon flashing, drag it to the intersection point of the three circles. When you are satisfied that you have placed it in the correct position, record the latitude and longitude displayed for this location in the placemark window.
(c)
Click “OK” to fix the epicenter into place.
3
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Before you begin: Create a folder in Google Earth to save all your work. You will send this folder to your instructor by email. To create a folder;
(a)
Click “Add” on the Menu Bar at the top of the window and select “Add Folder”.
(b)
Name the folder as shown: “YourLastName-EarthquakeLab”.
(c)
Select this folder when adding a placemark and it will be saved automatically to
this folder.
(d)
Any saved item that does not appear in this folder automatically can be added to the folder by clicking and dragging the item to the folder.
Exercise 1 – Earthquake in North America
On Monday, October 22, 2018 at 2:16 am, an earthquake with a Magnitude of 6.8 was recorded by seismographs at seismic stations in North America. The locations of the seismic stations and their distance to the epicenter are provided in Table 1 below.
Location
Station Name
Location Coordinates
(Latitude, Longitude)
Distance to Epicenter (Km)
Seattle, WA
KDK
47
O
36’ 14” N, 122
O
19’ 58” W
276
Portland, OR
DREG
45
O
31’ 23” N, 122
O
40’ 45” W
198
Missoula, MT
MSO
46
O
52’ 55” N, 113
O
59’ 32” W
860
Table 1. Seismic stations in North America by name and location, and their distance to the epicenter.
1.
Plot the location of each of the above stations, save the locations, and rename each one with its 3-letter code (eg. KDK). [6] 2.
For each station, plot a circle with a radius that is equal to the distance to the epicenter. [3]
3.
What is the location of the epicenter for the earthquake in North America (latitude,
longitude)? [2]
4.
What type of plate boundary or tectonic setting is responsible for this earthquake? (Be specific, eg. oceanic-oceanic convergent, etc.) [3]
5.
Based on the location of the epicenter, what specific earthquake hazard can be expected to affect the surrounding area? Explain your answer. [3]
Exercise 2 – Earthquake in Africa
4
An earthquake occurred on the continent of Africa and was recorded by three seismic stations in Mogadishu, Djibouti, and Addis Ababa. The data from this earthquake recorded at three seismic stations is provided below.
Location
Station Name
Location Coordinates
(Latitude, Longitude)
Mogadishu
MDU
2
O
2’ 42” N, 45
O
19’ 7” E
Djibouti
DBT
11
O
49’ 4” N, 42
O
35’ 23” E
Addis Ababa, ADAB
8
O
58’ 51” N, 38
O
45’ 28” E
Table 2. Seismic stations in Africa by name and location.
6.
Plot the location of each of the above stations, save the locations, and rename each one with its 3-letter code [6]
7.
For each station, record the P-S interval and the maximum amplitude. [6]
P-S Interval: _____________ seconds
Amplitude: _______________ mm
5
P-S Interval: _____________ seconds
Amplitude: _______________ mm
P-S Interval: _____________ seconds
Amplitude: _______________ mm
6
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8.
Using the Distance/Time graph above, determine the distance to the epicenter for each station and record this data in Table 3. [3]
Location
Station Name
Location Coordinates
(Latitude, Longitude)
Distance to Epicenter (Km)
Mogadishu
MDU
2
O
2’ 42” N, 45
O
19’ 7” E
Djibouti
DBT
11
O
49’ 4” N, 42
O
35’ 23” E
Addis Ababa, ADAB
8
O
58’ 51” N, 38
O
45’ 28” E
Table 3. Seismic stations in Africa by name, location, and distance to the epicenter.
9.
Plot the circles to determine the epicenter of the earthquake. [3]
10.What is the location of the epicenter for the earthquake in Africa (latitude, longitude)? [2]
11.Using the nomogram provided, and the seismograph from the Mogadishu
station,
determine the magnitude of the earthquake. [3]
Magnitude: _____________
12.What type of plate boundary or tectonic setting is responsible for this earthquake? (Be specific, eg. oceanic-oceanic convergent, etc.) [3] 7
Exercise 3 – Earthquake in Asia
On September 22, 2019, an earthquake occurred in Asia near Chame, Nepal, and was recorded by seismograms in China, India, and Pakistan. The locations of the seismic stations and their distance to the epicenter are provided in Table 3 below. Location
Station Name
Location Coordinates
(Latitude, Longitude)
Distance to Epicenter (Km)
Xi’an
XAN
34
O
1’ 53” N, 108
O
55’ 25” E
2,403
Nagpur
IMDN
21
O
6’ 7” N, 79
O
3’ 43” E
996
Karachi
KCHI
24
O
55’ N, 67
O
8’ E
1,758
Table 2. Seismic stations in Asia by name and location, and their distance to the epicenter.
13.Plot the location of each of the above stations, save the locations, and rename each on with its 3-letter code. [6] 14.For each station, plot a circle with a radius that is equal to the distance to the epicenter. [3]
15.What is the location of the epicenter for the earthquake in Asia (latitude, longitude)? [2]
16.What type of plate boundary or tectonic setting is responsible for this earthquake? (Be specific, eg. oceanic-oceanic convergent, etc.) [3]
17.The village of Chame in Nepal is located at 28
O
33’ 7” N, 84
O
14’ 25” E. Observe the location of Chame by zooming out, tilting, and rotating the map view. Based on
the location of the epicenter, what specific earthquake hazard can be expected to affect this village? Explain your answer. [3]
NB. To complete this exercise, you should now answer questions 13 – 30 at the end of Lab 14 in the Lab Manual (pages 124 – 126).
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