Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Jenna Lathrop
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
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.