AALL Internet Lesson

AALL Internet Lesson: Earthquake!
Student Online Activity Sheet
You just finished a discussion with your teacher and other students in your class. Several of the questions asked were: Have you ever experienced an earthquake? What did you do? How did you feel? Was there any damage? What would you do if there were one here now?
In this lesson you will explore numerous websites to find what causes earthquakes, what safety measures should you take in the event of an earthquake and why.
You will see new vocabulary words in this lesson. Here is a list of some of those words. Some of the definitions are listed alphabetically in a glossary that will require you to page through it to find the word.

plate tectonics
plate
fault
fault line
fault plane
focus ( Geology meaning)
rupture zone
hypocenter
epicenter
P wave
S wave
seismic
magnitude
intensity
hliquefaction
haftershock
lithosphere
subduction

You should find definitions in the link below:
Glossary
Take a look at Today in Earthquake History to see what events happened today in history, or for fun you may wish to check your birthday.
Some areas, California, for example, seem to experience many earthquakes and others experience very few.

To read the answers to the most frequently asked questions about earthquakes, see FAQ To read about what actually may cause the plates to move and whether we see this action other places in the solar system see Some Unanswered Questions

“What causes earthquakes?” was a question that geologists asked themselves for centuries, and it has only been answered in the last fifty years. Like many great questions in science, however, it wasn’t someone studying earthquakes who stumbled on to the truth, but someone looking at maps. Read the USGS publication Historical Perspective
Dutch map maker Abraham Ortelius noticed as early as 1596 that South America and Africa seemed to fit together, as did North America and Europe.
Based on the thinking at the time, he thought that the continents were pulled apart by
___________________________________. This belief that all earth changes are sudden and caused by disasters is called _______________________. Today we believe “The present is the key to the past.” and this belief is also called ______________________.

Of course, no one really bought the idea that the continents moved until 1912. In that year ___________________________ published his theory of continental drift. Not only was his theory based on the fit of the continents, but also on __________________________ and dramatic climate changes that seemed to have happened on some continents, shown by fossil tropical plants in Antarctica, for example.
Despite this evidence to support his theory, most scientists in his time thought the notion of moving continents was preposterous. What he failed to do was explain how the continents moved. That would take another thirty or forty years, and even then the evidence wasn’t found by people trying to explain earthquakes!

Read Developing the Theory. There were two things believed about the ocean floor that were proved wrong in the twentieth century. First, scientists believed the ocean floor was a
flat, featureless plain. Second, they believed the ocean floor was four billion years old and had been filling up with sediments (sand, silt, gravel) for all of that time. In reality the ocean floor has __________________________ running down the middle
of it and in the middle of this the ocean floor crust is not only not four billion years old, but is new. Volcanic eruptions here are creating new crust all the time, causing the Atlantic Ocean floor to become ever larger. This is known as _______________. The problem with this idea seemed to be: how could the earth keep expanding in places without actually getting larger? Harry H. Hess, a Princeton University geologist, came up with the explanation that as the earth expanded at the mid-ocean ridges, it got smaller as oceanic crust descended into oceanic ________________________. These are located mostly ___________________________________________.
Twentieth century improvements in detecting earthquakes (with seismographs) allowed scientists to map the locations of earthquakes.
Compare the map of tectonic plates to the map Global earthquake epicenters, 1963–1998" You may want to pay particular attention to the west coast of North America and the central Atlantic. How do the plate boundaries compare to where earthquakes happen?... it becomes obvious that the earthquakes happen at the ________________________(like in the mid-Atlantic) and in the _______________(like along the Aleutian Islands) which seems to support Hess’s theory. Magnetic banding of the volcanic rocks of different ages, with the ages older and older as one moves away from the mid-ocean ridges, and the bands “mirrored” on each side of the ridge also supported the theory of seafloor spreading.
Read Understanding Plate Motions to see how this knowledge has helped in earthquake prediction.
There are four types of plate boundaries:
Divergent boundaries are found where plates are moving ____________each other and new crust is created by _________________________________________ meaning that there are volcanoes along the boundary line. An example of where this is happening today is _________________________.

Convergent boundaries are found where two plates are moving ____________________each other and often one ____________________ under the other.
There are three scenarios for this
type of boundary:
1. Oceanic crust meets continental crust: the oceanic crust is denser and colder and is subducted under the continental crust. An example of a place where this is happening is
_______________________________. Just off the coast there is a deep _______________ and inland the continental plate is lifted up creating the __________ mountains complete with strong, destructive earthquakes, rapid uplift of mountains and many active volcanoes. A place in the United States where this is also occurring is _________________________________________.

2. Ocean crust meets ocean crust: one plate is subducted under another, again creating trenches and volcanoes, only in this scenario, the volcanoes form __________________. The __________________ Islands (part of Alaska) were formed in this way.

3. Continental crust meets continental crust: neither plate is subducted, instead the continental plates buckle and fold, forming mountains. The best example of this happening today is the __________________ mountains formed by the collision of ___________________ with ________________________.

Transform boundaries are found where two plates are sliding horizontally past each other, much the same way as your hands would move if you laid them side by side on a desk and pushed one away from you while you pulled the other toward you. This is what is happening at the famous ___________________ fault in California.
If the movement on the faults was smooth and continuous, there would be no “big ones” to worry about. To get a better look at why this doesn’t happen see here)

Plate boundary zones are called zones because there is no clear boundary line. There are often several plates and pieces of plates involved. There are complicated earthquake patterns. One example of such an area is where the ________________ plate meets the _________________ plate in the region of the Mediterranean and helps to form the Alps.

While we can predict how fast plates are moving, we still cannot predict the time and place of an earthquake. We are good at keeping track of those that have happened, however. See

Compare this map Global Seismic Hazard Map. How do they compare? _______________________________________________________
____________________________________________________________________________________

On the map (on the word map) find your state and your approximate location in it. Rate your predicted hazard (low, medium, high) _______________.

So what can you do if you are in an area when an earthquakes strikes? Read
FEMA recommendations for what to do during an earthquake
Other suggestions may seem to be counter to advice you have heard in the past. Isn’t the doorway the safest place to stand?...only if you live in an old adobe home where the walls are a foot and a half thick.

Click on photo 2 for a good look or have a look at the front of the building in this 1906 San Francisco photo which is at the bottom of the page.) If there were an earthquake at this moment, where would you go in this room to stay safe?
____________________________________________________________________________________

And suppose you decide to build or buy a home in an at-risk area. What are some of the things you should do to protect yourself, your family, and your friends?

Examine and read what happens when you don't build earthquake safe homes here Read FEMA'a guide for what to do before an earthquake

Now look around the room you are in and pretend it has been transported to the heart of earthquake country. What are some of the things you would want to change about the room?
___________________________________________________________________________________
___________________________________________________________________________________

How do scientists determine how big an earthquake was? Magnitude of an earthquake tells us that scientists now compare earthquakes by looking at magnitude which is proportional to_________________________________________________________________________________.
In general, the larger the magnitude , the _____________ the earthquake lasts and the _______________ the area it is felt in.
A “major” earthquake has a magnitude of between _________ and _________, and a “great” earthquake has a magnitude of __________ or more.
What you feel, however, may not correspond to the magnitude of the earthquake. . Although magnitude plays a part, two other things help determine what you might feel during an earthquake: _____________________________ and
_____________________________________. You don’t want to be in an area of loose, thick soil in case of an earthquake. Of course, this is exactly what many live on in Arizona.

To see what happens to homes built on soil, check Effects of building on fill; fill is usually soil brought from other places to “fill in” a depression. Fill and loose soils, especially if wet, undergo a process called liquefaction in which they act very much like quicksand. You can see some what happens atphotos 84-88