Yuma County has the highest risk statewide of experiencing a major earthquake, a fact coming back to the forefront following the large quakes and thousands of aftershocks recorded near Ridgecrest, Calif. on July 4 and 5.
Its proximity to California, and in particular the Imperial Fault which runs along the eastern side of the Salton Sea, means it would likely be affected if a magnitude 7 or greater earthquake struck there.
And that definitely could happen. "Their earthquakes are big enough to rupture the Earth's surface like these ones just now (in Ridgecrest), and obviously you're still a ways from it in Yuma, from the worst effects of it, but close enough to get some damage," Arizona State Geologist Dr. Philip Pearthree said Thursday.
On top of that, the moist, sandy soils found in the the Yuma and Gila valleys are the type which could lose their firmness and act like a liquid during a major seismic event, according to "Arizona is Earthquake Country," a booklet released by the Arizona Geological Survey in 2012.
This "liquefaction" effect could magnify damage to roads and buildings in areas which lie west of Avenue B or along the Gila River north of Interstate 8, according to a map in the book.
This kind of damage was reported after a major 1940 earthquake in the Gadsden and Somerton areas and into western Yuma, believed to have been about a 7 in magnitude. "There weren't as many people living in Yuma then, but there was damage to canals, and agricultural infrastructure, at that point," Pearthree said.
Another temblor, somewhat less powerful, hit the same area in 1979 and caused minor damage, he added.
In 2010 the 7.2-magnitude Easter Sunday earthquake, with an epicenter about 40 miles southeast of Calexico in Baja California, caused a power outage for 4,900 APS customers and shook items off many grocery store shelves, according to Yuma Sun reports at the time.
The city of Yuma set up an emergency operations center as a precaution, but no major damage or injuries were reported. Just across the border in San Luis Rio Colorado, Son., about 150 homes were destroyed or damaged.
Large aftershocks were felt in Yuma in June and September, but caused no major damage.
That incident inspired Yuma County officials to get on board with the Great California ShakeOut, an October earthquake preparedness drill which started a few years earlier, popularizing the phrase "Drop, Cover and Hold On."
Since then, the county has had some of the best participation in that event for the state as it has grown into the Great Arizona ShakeOut, Yuma County Emergency Management Director Tony Badilla said.
More than 38,000 residents participated last year, 5,000 more than in Maricopa County, according to figures Badilla provided. And more than 16,000 have committed so far to this year's event Oct. 17.
The University of Arizona-based Arizona Geological Survey is working to raise awareness statewide through the re-establishment of the Arizona Council on Earthquake Safety.
Lead Research Scientist Mike Conway said most Western U.S. states already have a similar panel, and Arizona briefly did in the-1990s before funding fizzled out.
"We need a platform from which experts can can talk to the people about earthquake risks and be heard," he said.
For more information about the upcoming Great Arizona ShakeOut, visit www.shakeout.org/arizona.