What are Earthquakes?

It is inevitable that a powerful and massive earthquake will strike California. How disastrous it is, is ultimately up to us; the more we prepare the better we’ll be able to handle it.  This is my first post in a series on understanding the earthquakes of our planet, and how we make sure to survive and thrive when a catastrophic one occurs. Even though this series will include statistics on the “big one” in California, this information applies to everyone around the world.

In 2008, the United States Geological Survey released a report forecasting California’s earthquakes stating that:

“There is a more than a 99% probability in the next 30 years for one or more magnitude 6.7 or greater [earth]quake capable of causing extensive damage and loss of life.  The likelihood of at least one even more powerful quake of magnitude 7.5 or greater in the next 30 years is 46%—such a quake is most likely to occur in the southern half of the State. Building codes, earthquake insurance, and emergency planning will be affected by these new results, which highlight the urgency to prepare now for the powerful quakes that are inevitable in California’s future.” (United States Geological Survey).

It’s apparent that an earthquake is coming, but what exactly is an earthquake?


What is an Earthquake?


If we took out a section of the Earth, shaped like a slice of cheesecake, we would find that it looks like this:


Crust, Mantle, Outer Core, Inner Core  (2)             Earth cross-section(3)

We can see the four layers: the inner core, outer core*,  mantle, and the crust. The upper portion of the mantle and the crust are collectively known as the Lithosphere. The Lithosphere is not one one long continuous piece;  it is composed of large puzzle pieces. These puzzle pieces are known as Tectonic plates, and act like moving walkways carrying land masses and oceans along.


* Scientists believe that the movement of the molten metals of the outer core creates Earth’s magnetic fields, or the Geomagnetic field.  Over time, the Geomagnetic field changes (the north and south poles swap).  As the magnetic fields changes, so does the direction of magnetic minerals face.  This proves to be a useful dating method for Anthropologists and Geologists.


Earth’s Tectonic Plates (4)


The tectonic plates are like old people impersonating bumper cars, slowly moving around and running into each other  (It is not well understood why the plates move).   The perimeter of the plates are known as plate boundaries, and are made up of many fault zones.  Fault zones are collections of fractures within and on the boundaries of the tectonic plates.  This is where the majority of earthquakes occur. Due to the coarse nature of the boundaries, the plates may adhere to one another while the rest of plate continues to move.  With enough movement the plates unstick to each other. The separation of the plates causes a surge of potential energy to be converted into kinetic energy in the same way that drawing on a bowstring causes potential energy to be stored through tension, and released to give flight to an arrow.


“The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us!” (3)


In essence, earthquakes are the energy that is released from the friction of sliding tectonic plates.  But what does this energy do, what kind of damage do earthquakes cause, and what are people talking about when they say an earthquake is a certain magnitude? We’ll talk about all of this in my next post in the series.  Feel free to any comments, questions, or concerns.





1. Field, Edward H., Milner, Kevin R., and the 2007 Working Group on California Earthquake Probabilities, 2008, Forecasting California's earthquakes; what can we expect in the next 30 years?:   U.S. Geological Survey, Fact Sheet 2008-3027, 4 p. [http://pubs.usgs.gov/fs/2008/3027/].

2. "OLogy." OLogy. American Museum of Natural History, n.d. Web. 07 Apr. 2014. [http://www.amnh.org/ology/features/stufftodo_earth/edible_main.php].

3. Wald, Lisa. "The Science of Earthquakes." The Science of Earthquakes. U.S. Geological Survey, n.d. Web. 06 Apr. 2014.

4. Lynch, David. "Plate Tectonics, Continental Drift, Spreading Centers, Subduction Zones." Plate Tectonics, Continental Drift, Spreading Centers, Subduction Zones. N.p., 2010. Web. 07 Apr. 2014

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