HW_USGS eq tracking-JRH
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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 on inferring the 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? -Pacific Ocean Region
2.
Are the places you listed associated with plate boundaries?
-Yes
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.
)
EES 0836
-Convergent
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?
-Most of the earthquakes with a magnitude was 4.5 or even higher have been in western parts of the USA.
5.
Does this make sense given the distribution of known active faults in the country? Why or why not?
-Yes, The Distribution makes sense reason why the presence of active faults in the southern part of the US. The west tectonic plates are active from the interactions between the Pacific Plate and North American Plate.
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?
- The relationship is inverse as larger earthquakes with higher magnitudes happened less frequently while smaller earthquakes with lower magnitudes
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)? -Higher magnitude earthquakes are more commonly associated with plate boundaries where tectonic forces are active.
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 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 earthquakes in Hawaii are caused by volcanic activity since it is located over a hot spot where magma rises to the surface, creating volcanic eruptions that are associated with seismic activity.
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.
EES 0836
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? 10.
Why do you think this relationship exists? (Hint: What’s the tectonic situation at this plate boundary?) This relationship exists because of the way the plate boundary moves at this location.
-This relationship exists because the trench is a subduction zone where one of the tectonic plates is being pushed beneath another. The deeper earthquakes are associated with the subduction of the Pacific plate beneath the North American plate, while the shallower earthquake is closer to the
trench where the plates are interesting.
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? - 0
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.
-The number of earthquakes would generally remain the same as the east coast of the United States is not as seismically active as areas near plate boundaries.
13.
Several geologic features 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.
-
You would see normal faults forming which are associated with extensional tectonic forces where the earth’s crust is being pulled apart. As a continent breaks apart forces cause the crust to fracture which creates normal faults where one block drops to the other.
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