The unpredictability of earthquakes is a jarring yet expected part of life for California residents. But when two early July SoCal temblors rippled through Southern Nevada, they left many local residents shaken up and looking for answers.
Few in the Las Vegas Valley realize that Nevada is the nation’s third-most seismically active state – behind California and Alaska – with active faults statewide capable of “the big one.” The last major quake with an epicenter in Nevada was a 6.0 magnitude event in 2008 in the small community of Wells. Many of the town’s structures were damaged, though thankfully no one was seriously injured.
Just how big is Southern Nevada’s earthquake risk, why did we feel the California quakes from more than 150 miles away, and how can we best prepare for future events?
We asked UNLV geoscientist Wanda Taylor, who has been investigating this topic for decades. Taylor and colleagues are now researching the Las Vegas Valley’s sediments and their relation to faults in and around Southern Nevada – work that may help them determine which of our half dozen or so active faults pose the biggest risk.
Many locals are surprised to find out that the earthquake risk is real in Nevada. Why is our region prone to earthquakes?
The earthquake faults in Nevada and Utah are considered intraplate faults, which means they’re located fairly near but not at a plate boundary.
The earth’s outer layer, or shell, is broken into pieces called plates. At a plate boundary, two plates move relative to each other, and this movement can cause earthquakes. The San Andreas fault – which stretches for roughly 750 miles in California – is the boundary between the North American and Pacific plates. In some cases, interactions between plates along the boundary cause them to deform and trigger earthquakes that can be felt for hundreds of miles.
In earthquake geology, a hazard is a source of potential harm or adverse effect and risk is the combination of the likelihood of the occurrence of a harm and the severity of that harm, which includes economic losses.
The Reno-Carson City corridor has a higher hazard than the Las Vegas metropolitan area because the faults there have more frequent earthquakes; however, the risk is higher in the Las Vegas Valley because the area has more buildings and infrastructure that could be damaged.
The early July earthquakes were more than 100 miles away in Southern California. Why did we feel them in Southern Nevada?
The amount of ground shaking from an earthquake relates to its magnitude and the distance from the epicenter – the larger the magnitude, the greater the shaking.
Generally, the earthquake waves that travel through the earth diminish with distance from the earthquake source area. Harder or stiffer ground will shake less than softer materials. The Las Vegas Valley is bounded by hard bed rock and is filled with softer sediments. Simply put, our valley (a.k.a. the basin) may shake like a bowl of gelatin with the bowl being the bedrock and the gelatin being the soft sediments. It is possible for this condition to amplify the earthquake waves, a phenomenon you may see referred to as the basin effect.
How many earthquake faults are in Nevada, and should we be worried?
Nevada has dozens of active faults, but, like we learned last week, an active fault more than 100 miles outside the Las Vegas Valley could also shake the area. Faults in Death Valley, particularly, pose a significant hazard to our community. We don’t believe the recent earthquakes impact our hazard locally.
Two types of faults are common in Southern Nevada: normal and strike slip. Along normal faults rocks above the fault move down relative to those below the fault. Along strike-slip faults the rocks across the fault move horizontally past each other. You can see fault lines throughout the Las Vegas Valley – along Decatur Boulevard, near Frenchman Mountain, and over by Cashman Field, just to name a few.
Geologists consider an active fault to be one that has generated an earthquake, has had observed movement, or shows other evidence of seismic activity at some point in the last 10,000 years.
Though earthquakes in and around Las Vegas aren’t as frequent as in California, the risk for a magnitude 6.0 or greater event is something we need to be prepared for. I give credit to officials in Clark County for updating building codes in the mid-1990s to increase seismic safety. We’ve come a long way in this area, with the resort community doing a particularly good job to meet or often exceed codes.
How can Southern Nevadans prepare for an earthquake?
There are numerous resources people can turn to for detailed tips on what to do during an earthquake and, importantly, how to plan for the hours and days following an earthquake. The Red Cross has a great website with safety tips and a checklist for developing an emergency preparedness kit and a household evacuation plan.
During an earthquake, remember to Drop, Cover and Hold On. Find a piece of furniture, like a table, to move under and hold onto it. Contrary to popular belief, doorways aren’t safe places during an earthquake. Stay inside until the shaking stops; if you’re already outdoors, move away from structures – including bridges, power lines, trees, and streetlights.
Every home should have a preparedness kit with essentials needed for you and your family to survive for three days. Kits should include one gallon of water per-day for each member of the household, non-perishable food, extra medications, a flashlight, and a first-aid kit. You can also prevent hazards in your home by strapping your water heater to the wall – which prevents fire and provides a source of potable water in an emergency, secure tall furniture such as bookcases to the wall, and avoid placing heavy objects over beds.
It's also a good idea to consider participating in earthquake preparedness drills each year to stay sharp. UNLV, through the Office of Emergency Management, participates in The Great ShakeOut, a worldwide partnership that hosts drills and educates local communities on ways to protect themselves during an earthquake.