1. University Primary School Champaign, IL January 13, 2011
Customize with name of school and date.

2. Plate Tectonics
How to Explain: Mountains, Volcanoes, Sea Floor Bathymetry
How do we explain the mountains that we see, the volcanoes that are erupting, the mountain ridges and basins under the ocean (sea floor bathymetry)? Plate Tectonics was discovered through our curiosity to understand these features on the Earth.

3. Tectonic Plates

5. Earthquake Epicenters Follow plate boundaries
Important evidence for plate tectonics is the location of earthquakes (and volcanoes) along the edges of all the Earth’s plates. Notice that the earthquake locations plotted as small blue dots on this map outline the major plate boundaries.

6. Plate Shapes and Seismicity
Compare the map we saw from before, with the map of the earthquake locations. For reference, the pacific plate is the large yellow plate to the left in the top map, and in the right-center on the bottom map.

7. crust is very thin! Hard Boiled Egg - Egg Shell=Crust
Earth
crust is very thin! Hard Boiled Egg - Egg Shell=Crust
We Earth Scientists use seismology to look into the Earth (imagine cutting a hard-boiled egg in half). This view is a cross-section with depth into the earth along the vertical axis, and distance along the surface along the top horizontal axis. You can see here the thin plates that are the crust, with the continents riding along on top. New crustal material is being formed at the oceanic spreading centers (volcanic ridge), and older crustal material is being recycled back into the Earth at subduction zones (deep ocean trench). This process is call the plate tectonic cycle.

8. 2008 Earthquakes > M5.5
This figure is a map of earthquakes detected by the National Earthquake Information Center (NEIC) in 2008, and is typically of earthquakes about M5.5 or larger. As you can see they are happening mostly along the same boundaries that we saw in the previous images. Almost all the earthquakes occur at plate boundaries.

9. Global Seismographic Network
This is a poster available from IRIS. This map shows the stations that monitor earthquakes all over the globe, including Antarctica, Iceland, all over the U.S., and in the oceans on islands and even the sea floor. On every continent we have seismometers. Those seismometers enable us to learn about the earthquakes themselves. What’s causing them? What are the stresses that are being released when they happen? They also give us a way of imaging the inside of the earth. We use the waves that are generated when there is an earthquake to study what’s inside the earth.

10. Earthquake Magnitude and Equivalent Energy Comparisons
How Many?
Earthquake Magnitude and Equivalent Energy Comparisons
In terms of the total number of earthquakes each year, there are millions. The last figure only had magnitude 5 ½ and above. In this figure we can see the total number of earthquakes, on average, in one year worldwide. This includes magnitude two and three. These earthquakes are happening all the time even here in California. Everyday, you can go to online resources and look at the most recent earthquakes for the last seven days, and every day there are little ones here in California that nobody can feel, but our sensors are sensitive enough to detect.
The San Francisco earthquake of 1906 was a great earthquake that did a lot of damage. Even so, this graph shows how much more energy the earthquakes in Chili and Alaska were. This chart was made before the Indonesia earthquake, which is a little smaller than Alaska.
The chart gives you lots of things to compare the energy released in an earthquake to. The small earthquakes that we can begin to feel have about as much energy as a bolt of lightening. If a magnitude 4.5 earthquake occurred beneath us, buildings and windows would shake briefly and things might fall from shelves. The chart shows that such an earthquake releases as much energy as a tornado.
Seismologists, the scientists that study earthquakes, have different ways of determining the energy released in a single earthquake. About the same amount of energy, in total, is released every year in earthquakes around the world. The graph indicates that there are about a million magnitude 2 earthquakes, which could be too small a number and the actual number may even be larger. In fact, there are a lot of earthquakes that are not recorded by any network. So the number of small earthquakes is probably larger. For great earthquakes, of magnitude 8 and above, there are only about three per year. For the very largest, magnitude 9, there is on average less than one a year.

11. Here’s another image from space and we’re going to zoom in
Here’s another image from space and we’re going to zoom in. This again is the coastline of California.

13. A fence built over a fault…
Let’s discuss what happens during an earthquake. At the bottom of this diagram is a fence that crosses the San Andreas Fault. The right side of the San Andreas fault is on the North American Plate. That is a few dozen miles to the East of us, here in Santa Barbara. The left side of the figure is the Pacific plate, where the cities of Santa Barbara, Los Angeles and San Diego are located. The Pacific Plate is moving towards the North while the North American plate, on the right of the figure, is moving South. As time progresses, the plates are in motion. At the boundary, the fault itself is locked. When enough movement has occurred that stress has built up on that boundary, the fault ruptures and causes an earthquake. We have brought a table-top simulator that uses a brick, sandpaper and elastic to demonstrate fault rupture. You will see the stress building up and then suddenly the bricks will move and that simulates an earthquake.

14. San Francisco Earthquake
1906
San Francisco Earthquake
Fence Offset
Above is a photograph that demonstrates the previous slide. We don’t have a picture of the fence before the quake, but we can assume that it was built in one straight line. This picture was taken after the 1906 earthquake in San Francisco and you can see there’s an offset of a couple of meters. The fault shifted the fence, the earthquake “ruptured” through to the surface and the ground around the fault was displaced by the earthquake.

15. Here is a satellite view looking down at the earth’s surface
Here is a satellite view looking down at the earth’s surface. The Gulf of California and Baja California are on the lower left. The coastline of California moves up along the left and Los Angeles is near the center of the picture. The lines represent quake boundaries coming up through the Gulf of California, through the Imperial Valley and Salton Sea. North of Palm Springs is the San Andreas fault which bends to the West. This is often called the “big bend.” The stresses in the earth created by the plates moving around this “bend” create the mountains around Santa Barbara and Malibu. This bend is also called the transverse region. With the Pacific plate moving northward and the North American plate moving towards the south, the plates “buck up” against each other and that pushes up the mountains. Santa Barbara has beautiful mountains behind it to the East. These mountains were created by tectonic stresses in the earth that are the basis for both the mountains and earthquakes. There is another fault offshore of Santa Barbara. This fault continues underneath the mountains and is continuously pushing up those mountains. There could be a magnitude earthquake in Santa Barbara at any time. A magnitude 6 or larger earthquake can seriously damage an old building. Wood frame homes, on the other hand, are usually not damaged by such quakes although objects can fly off shelves. Wood frame construction is very ductile, which means it can sway and move around. The nails used to hold wood frame houses together are long and there is a lot of bracing to prevent houses from falling down. The building codes in California have been developed to insure that homes can withstand these motions and inspectors guarantee that the contractor has followed them when they built your house.

16. Earthquakes travel around the world.

17. Ask audience – this is a thermometer, to measure temperature

18. Ask audience – this is a speedometer, to measure speed

19. Ask audience, this is a seismograph with a seismometer, which measures ground acceleration and the intensity of an earthquake.

20. Seismometer Measures Earthquakes
How do we actually measure earthquakes? This is a very simplified diagram of a seismometer. When the earth shakes, the weight attached to the spring mostly remains still, while the drum moves up and down. The pen on the weight records the movement. An actual seismometer, such as the one we brought to show you, uses a magnetic coil that is wrapped around a magnet inside. When the magnet moves up and down, it generates electricity in the coil and that electricity is then recorded and saved by a computer so we can look at it or print it out. In our demonstration, you will jump, see the earthquake you created on a computer screen and receive a print out with your name on it. The process is more complicated than described and we have simplified it for the demonstration today.

22. This is a MEMS device – like the accelerometer where you can make-your-own-earthquake .