Earthquakes Lab Doc
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California State University, Fullerton *
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101L
Subject
Geology
Date
Jan 9, 2024
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6
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ANSWER SHEET FOR EARTHQUAKES LAB
WHERE DO EARTHQUAKES OCCUR?
The best way to find where earthquakes occur is to look at a map of earthquakes. Go to the
USGS earth-quake web page (
earthquake.usgs.gov
; Figure 6.5). This website contains a lot of
information and you should, at some point, explore it. Each of the 6 tabs at the top (Earthquakes,
Hazards, Data & Products, Learn, Monitoring, and Research) will give you more extensive
information about earthquakes around the world. We are going to use the Latest Earthquakes
interactive map.
Click anywhere on the Latest Earthquakes map
(Figure 6.5).
Figure 6.5
That should take you to the interactive map page (Figure 6.6), which has two panes: a map (right
pane) and list of earthquakes (left pane). Go to the World View by selecting
World
in the
Zoom
to Region
drop-down menu (the little globe button beneath the +/- tabs). The oceans are gray;
continents white; red lines are tectonic plate boundaries.
Figure 6.6
This map (Figure 6.6) is updated within minutes of an earthquake, so your map will not look
exactly like the one shown. The default map shows all earthquakes in the last 24 hours with a
magnitude greater than 2.5. Go to
Settings
(the gear, top right) and change the earthquake display
settings to
30 days, Magnitude 2.5+ Worldwide.
Your map should update to show every
earthquake that has happened in the past 30 days.
A.
Using the Interactive map of world-wide earthquakes (Figure 6.6; Settings: 30 days, M>2.5),
describe the general distribution of earthquakes. About how many are there? Are there clusters?
The earthquakes are distributed mainly along the tectonic plate boundaries. There are
1,657 earthquakes shown on the map. Yes, there are a number of clusters of earthquakes
depicted on the map.
B.
Use the
Zoom to Region
menu again to select U.S. Make sure you are still in the 30 days,
Magnitude 2.5+ Worldwide setting.
Where are (is?) the plate boundaries within the lower 48 states of the United States? List the
states on or near (300 km) of plate boundaries.
The plate boundaries with the lower 48 states go through/boarders the states on the west
coast of the country. The states within 300km of the plate boundaries include California,
Washington, Oregon, and Arizona.
C.
Are all of the earthquakes in the lower 48 states along the plate boundary (boundaries)? List
the states where earthquakes have occurred in the last 30 days.
No, all the earthquakes in the lower 48 states do not only occur along the plate boundary.
The states where earthquakes have occurred in the last 30 days include Washington,
California, Nevada, Idaho, Utah, Wyoming, Colorado, New Mexico, Texas, Kansas, South
Dakota, Oklahoma, Tennessee, Missouri, Illinois, North Carolina, Oregon, and Montana.
D.
In the
Settings
pane, click on the layers tab (the tab with three layered panels on it), then click
on the U.S. Hazards checkbox. Warmer colors are high earthquake hazard areas; cooler colors
are low earthquake hazard areas. List the states that have higher-risk (red, orange) earthquake
hazard zones. Are there earthquakes in each hazard zone in the last 30 days? If not, what state in
a high hazard zone has not had an earthquake?
The states that have a higher-risk of earthquake hazard zones include California, Nevada,
Montana, Washington, Oregon, Idaho, Wyoming, Kentucky, Missouri, Arkansas, and
South Carolina, Utah, Colorado, Oklahoma. No, not every state that has a higher-risk
hazard zone has had an earthquake in the last 30 day. For example, the states with a high
hazard zone that have not had any earthquakes in the last month include Arkansas and
South Carolina.
E.
Use the
Zoom to Region
pull down menu again to select California. Once you zoom to
California, uncheck the U.S. Hazards box and check the U.S. Faults box. If you move the mouse
over a red line (a fault), the fault name will appear.
Describe the relationship between fault lines and earthquakes in California. Where do the
greatest number of earthquakes occur?
Fault lines and earthquakes in California have a relationship of sticking together.
Furthermore, the greatest number of earthquakes in California occur along/in the general
region of a specific fault line, the San Andres Fault.
F.
The colored dots are earthquake epicenters. Click on 12 different epicenters in California and
record the depth in kilometers of each in the table below.
Include the depth units!!!
1.
-1.8 km
2.
9.5 km
3.
4.3 km
4.
4.7 km
5.
3.1 km
6.
9.4 km
7.
16.6 km
8.
8.2 km
9.
6.4 km
10.
6,9 km
11.
5.5 km
12.
13.2 km
Minimum Depth:
-1.8 km
Maximum Depth:
16.6 km
Average Depth:
7.16 km
G.
On the Latest Earthquake map, zoom in to Alaska (Figure 5.7).
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Figure 6.7
Click on 12 different epicenters along the Aleutian Islands
(the “tail” of Alaska)
. Make sure that
you click on epicenters both north and south of the Aleutian Islands. Record the depth in
kilometers of each earthquake in the table below.
Include the depth units!!!
1.
95.5 km
2.
80.1 km
3.
98.8 km
4.
10 km
5.
35 km
6.
20.8 km
7.
10 km
8.
22.5 km
9.
105.7 km
10.
101.4 km
11.
9.3 km
12.
10.7 km
Minimum Depth:
9.3 km
Maximum Depth:
105.7 km
Average Depth:
49.98 km
H.
Do the plate boundaries at California and Alaska have similar earthquake depths? Why or
why not? What could explain the differences or similarities?
The plate boundaries at California and Alaska share some similar depths, however most of
the earthquake depths for Alaska are significantly deeper than those of California. I believe
that this difference in de
pths could have to do with the fact the most of Alaska’s epicenters
occur in the ocean and underwater, allowing for the depths to be much deeper than those
epicenters of California’s which occur on land
.
EARTHQUAKE INTENSITY AND IMPACT.
I.
Zoom into southern California with the
30 days, Magnitude 2.5+
setting still active. Click on
the epicenter closest to where you live. This will make
a blue hyperlink (“M##
- #km from Place,
CA”) appear in the bottom left of the screen: follow that link, then proceed to “Did You Feel It?”
page. Using that page, record the following pieces of information:
Magnitude:
2.5
Location Description:
2km SW of Willowbrook, CA
Maximum Modified Mercalli Intensity (DYFI):
2.3
Date & Time:
October 12, 2023, at 8:38 am
Depth:
22 km
Based on the Did You Feel It map, does it seem like a lot of people felt this earthquake? Did it
cause much damage? Refer to the intensity scale beneath the map.
According to the Did You Feel It Map, it seems that 9 people reported that they felt this
earthquake happen. Provided with the number of responses to the earthquake, it seems
that not a lot of people felt it occur. According to the intensity scale beneath the map, there
was no damage caused by this earthquake.
J.
Consider two M7.1 earthquakes (identical amounts of energy released). One occurs in
California, the other occurs in Alaska, but the MMI in California is VIII whereas the MMI in
Alaska is IV. Why might California have a higher reported intensity than Alaska despite the
magnitude of the earthquake being the same?
California might have a higher reported intensity than Alaska, even though the magnitudes
of the earthquakes are the same, since California has many factors that would lead to a
difference in intensity. For instance, some factors that have the potential to cause a higher
intensity for California earthquakes include its closer proximity to epicenters, the
difference in geographic/geological conditions, and the effects that valleys, mountains,
lakes, and forests have on amplifying the earthquakes shaking.
K.
Consider another potential issue. Which area, California or Alaska, is at greater risk of
experiencing a tsunami? Why? To answer this, you may want to refer to your reading.
Alaska is at greater risk of experiencing a tsunami than California is. There is a greater
risk in Alaska because its trenches are offshore and have common seismic activity.
Furthermore, this means that powerful earthquakes can occur and then lead to tsunamis.
UNNATURAL EARTHQUAKES.
L.
In recent years, oil field operations have used the process of fracture injection or
fracking
. A
frequent complaint about fracking is that it produces earthquakes. Fracking is commonly done in
the Oklahoma area. What are the relationships between epicenters and fault lines in Oklahoma in
the last 30 days? What magnitude and depth are the earthquakes?
The only fault line that is shown as being in Oklahoma is Meers Fault. It seems that there is
not a relationship between Meers Fault and the two earthquakes that have occurred in
Oklahoma in the last 30 days since they occurred approximately 200km-300km away from
the fault line. The magnitude of the earthquake that occurred on October 14
th
is 2.9 and the
depth is 16.1 km. For the second earthquake, which occurred on October 15
th
, it had a
magnitude of 2.5 with a 7.9 km depth.
M.
How would you
distinguish between fracking earthquakes and “normal” earthquakes in
California? What could you do to investigate the cause of different earthquakes?
In order to distinguish between fracking earthquakes and “normal” earthquakes that
occur in California, you must look at many different factors. Furthermore, to make the
distinction between the two types of earthquakes you should first consider and analyze the
different depths, areas of occurrence, and seismic patterns. To investigate the cause of
different earthquakes one would have to conduct analyses on seismology.
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