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Roger Weller, geology instructor

earthquake potential
by Jenna Lathrop
Physical Geology
Spring 2017

    Could Sierra Vista Be Devastated By An Earthquake?

     Though not always considered to be a threat, there were nearly five hundred earthquakes in and around Arizona in the last year, and in the last 150 years there

 there have been 20 that were a five or above on the Richter Scale.  Obviously the vast majority are barely felt- if felt at all- but some are much more devastating.

    So, what are earthquakes and why do they occur?  An earthquake is caused when rock underground suddenly breaks, or in other words, a sudden release of energy underground usually associated with fault or magma movement.  The sudden release of energy is what causes the ground to shake.

Earthquakes are measured on what is called the Richter Scale, which is described here:


    Arizona has been affected by several earthquakes, as stated earlier.  In 1887, for example, there was a terrible earthquake with a magnitude of 7.4 on the Richter scale that occurred just 200 miles south of Sierra Vista.  The Sonora Earthquake is one of Arizona’s most devastating earthquake, even though the epicenter was located in Sonora, Mexico.  Douglas, which is a part of Cochise County, was devastated by the earthquake.  Damaged buildings were reported as far away as Phoenix. This earthquake was responsible for 51 deaths as well as extensive property damage.

    There are a few fault lines in the southern Arizona area, as shown below.  However, they are all small so it is highly unlikely, to the point of being virtually impossible, that the epicenter of any earthquake would be located in the southern Arizona/Sierra Vista area.


    However, the San Andreas fault, or the sliding boundary between the Pacific Plate and the North American Plate, is located in the Southern Arizona area.  It is only 80 measly miles west of Yuma, which is only around 300 miles away from Sierra Vista. The fault is shown here:


    If a massive earthquake were to occur in the southern California area, which experts think will happen soon, Yuma would definitely feel the effects of it.  Its old buildings would most likely crumble.  Depending on the size of the earthquake, Sierra Vista could also feel some of the effects from the earthquake or its aftershocks, but to a far less serious extent.  It would not be devastating and would probably not cause much, if any, damage.

    Because of all of this, it is important to be able to recognize an impending earthquake.  Even though an earthquake will probably not ever devastate this area, it is always better to be informed and prepared.  Though it is not entirely possible to predict them, there are warning signs that can be used as indicators that one is coming.

    Animal behavior being used as an indicator for an earthquake was first reported in 373 BC Greece.  Reportedly, rats, weasels, snakes, and centipedes left their homes days before a devastating earthquake to head for safety.  Stories like this one are still considered today, as animals are closer to the ground and do not wear shoes.  It is thought that dogs bark more and horses look panic stricken before an earthquake, but it is hard to measure. It is a common belief that they have a keener sense of what is going on below the Earth’s surface.

    Other indicators include static on the radio, the phenomena of light emanating from the ground, and studying earthquake patterns themselves.  Earthquakes usually occur about every thirty years, so it is possible to loosely predict when another one will occur.

    Overall, it seems that Sierra Vista could not and will not be devastated by any earthquakes.  Its location away from major fault lines nearly ensures it.  It is possible that it could be affected by an earthquake or its resulting aftershocks, but no real or lasting damage would occur.