HW_USGS eq tracking
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EES 0836
USGS Earthquake Tracking Assignment
Disasters: Geology vs. Hollywood
Introduction
Just because most earthquakes are not felt by people doesn’t mean they do not happen. Because we have
seismic stations located throughout the United States (and beyond), we know that earthquakes happen all
of the time. This exercise uses the U.S. Geological Survey’s “Latest Earthquakes” map, which is updated
every couple of minutes, to help reveal the frequency of these events.
Learning Objectives
●
Describe the value of an earthquake's epicenter and focus to infer tectonic processes driving them.
(3, 5, b, c)
●
Identify the relationship between magnitude and frequency.
(3, 5, d)
Part 1:
U.G. Geological Survey map
Follow these initial instructions to get started, then answer the series of questions below based on the data
on the website.
A.
Navigate to
https://earthquake.usgs.gov/earthquakes/map/
B.
The “Zoom to…” box in the upper right of the map will allow you to quickly navigate to
different places. Start by selecting “World”.
Note: The continents repeat in this view, but zooming in to the next level cuts off some of the
whole picture, so we’ll stay here for now.
C.
Click on “show legend” at the bottom of the map.
a.
Each circle represents an earthquake epicenter.
b.
The magnitude of the event is reflected in the size of the circle.
c.
The color of the circle indicates the age of the event.
d.
Clicking on any circle will bring up the stats for that particular earthquake on the bottom
left of the page.
D.
Feel free to look around to familiarize yourself with the page. If you do change the information
displayed, make sure you default back to the information we started with in A.
Questions:
Let’s start by examining the overall global pattern of earthquakes, magnitude 4.5 and over, in the last 30
days.
1.
In what geographical area(s) do most of the earthquakes on the map cluster?
Most of the earthquake’s cluster in the southern part of Asia, or in Mexico or Brazil.
2.
Are the places you listed associated with plate boundaries?
Yes, these areas of interest are associated with plate boundaries.
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3.
If you answered yes to Question 2, what type of plate boundaries (divergent, convergent,
transform) are they? (
If you answered no to Question 2, skip this question.
)
The North American plate, as well as the Cocos plate, are convergent boundaries, while the
Caribbean plate is a complex transform plate.
Locate the “Zoom to…” menu in the top right of the page and select “U.S.”
4.
In the last 30 days, have most of the earthquakes of magnitude 4.5 or higher been in the western,
central, or eastern part of the country?
In the past 30 days, there have been two earthquakes of 4.5, juts north or Sacramento, in th
western part of the country.
5.
Does this make sense given the distribution of known active faults in the country? Why or why
not?
Since earthquakes are very common in the west due to the plate boundaries, this makes total
sense.
Using the gear icon in the top right of the page, change your setting to “30 Days, Magnitude 2.5+ U.S.”
Click back and forth between the “Magnitude 4.5+” and “Magnitude 2.5+” settings a couple of times to
get a sense of how the number and geographical distribution of earthquakes changes when you include
the smaller magnitude events. Finish at the “Magnitude 2.5+” setting.
6.
What can you say in general about the relationship between earthquake magnitude and frequency
of occurrence?
There are much more earthquakes of 2.5+ than 4.5+, telling me that earthquakes of less
magnitude occur much more frequently.
7.
What can you say in general about the relationship between earthquake magnitude and whether it
occurs on a plate boundary or not (intraplate earthquakes)?
Earthquakes tend to happen much more frequently in the plate boundaries due to the tectonic
plate movements in that area, ranging in magnitude.
On the “Zoom to…” menu, now select “Hawaii”. Click back and forth between the “30 Days, Magnitude
4.5+” and “30 Days, Magnitude 2.5+” settings a couple of times again to get a sense of how the number
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and geographical distribution of earthquakes changes when you include the smaller magnitude events.
Finish at the “30 Days, Magnitude 2.5+” setting.
8.
Hawaii is the most seismically active state in the U.S., even though it is not on a plate boundary,
but the quakes tend to be small and very geographically concentrated. What is the source of the
earthquakes in Hawaii?
The source of the earthquakes in Hawaii are due to the heavy volcanic movement, and magma formation.
Looking at the map, there have been no earthquakes of a 4.5 magnitude or higher in the past 30 days, bu
there has been many earthquakes of a 2.5 or higher in the area.
On the “Zoom to…” menu, now select “Alaska”. Change the magnitude setting back to “30 Days,
Magnitude 4.5+” to get a more manageable data set. We are going to focus on the earthquake epicenters
along the Aleutian Trench and the plate boundary associated with it.
9.
Click on the circles for the individual earthquake epicenters in the general region of the trench.
When the stats for each earthquake come up, pay particular attention to the “Depth” information.
This tells you how deep below the surface the actual focus of the earthquake was. You should be
able to notice a general relationship between the depth of the earthquake foci and the distance of
the earthquake from the trench itself. What is that relationship?
The deeper the earthquake is into the Bering Sea, the greater the depth of the quake, ranging from
34 km to 180 km deep.
10.
Why do you think this relationship exists? (Hint: What’s the tectonic situation at this plate
boundary?)
The tectonic plate movement is greater the deeper you get in that specific area.
Now draw your attention to the east coast of the United States. Change your magnitude setting to “30
Days, Magnitude 2.5+U.S.”
11.
How many earthquakes have occurred here in the past 30 days?
There was one in Montreal, besides that, there have been no earthquake on the east coast that
were a magnitude of 2.5+.
12.
If you were to do this same assignment 30 days from now, would you expect to see more, less, or
about the same number of earthquakes in this region? Explain your thinking.
I would expect this area to have the same number of earthquakes a month from now, simply
because I don’t think much will change with the plate movements.
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EES 0836
13.
There are several geologic features that were produced when Pangea began to break up around
200 million years ago. Among these features are faults. What type of fault would you expect to
see forming during the breakup of a continent? Explain your reasoning.
During the breakup of the continent, I would expect normal faults to be forming, due to the divergent
boundaries.