SALT LAKE CITY (KUTV) — A string of more than 100 minor earthquakes near Bluffdale this month, many are asking just how much damage Utah buildings will sustain if a major earthquake strikes.
Utah Emergency Management decided to answer that complicated question in a series of 20 tweets.
"People want to know how much damage they will receive in a severe earthquake," Utah Emergency Management tweeted. "This is a question with a long answer. Buckle up. The damage a building receives during an earthquake depends on a number of factors."
Below is information taken directly from Utah Emergency Management's tweets:
- BUILDING CONSTRUCTION -- Wood-framed homes generally fare better than masonry, especially if masonry isn't reinforced. Most modern buildings, built after 1975, should be survivable, which means that they will stand up long enough for people to survive and evacuate. Buildings that survive major shaking may not be usable afterward, though. Aftershocks can bring down buildings that survive an initial shock. The Utah Seismic Safety Commission has a guide for retrofitting un-reinforced masonry homes at ussc.utah.gov. In older homes, the roof may not be connected to the walls, or the walls may not be tied to the foundation.
- EARTHQUAKE DEPTH -- Earthquakes can occur near the surface of the earth or quite deep. A strong earthquake that happens deep in the earth may not have the same impact as a weaker earthquake that happens near the surface. Deep earthquakes are felt over wider areas.
- DISTANCE -- The farther away you are from the epicenter, you are more likely to be better off during an earthquake. This is a rule of thumb. Energy dissipates throughout the earth, and less energy/shaking will reach you if you are far away. In our worst-case scenario quake centered in Salt Lake City, which has only been modeled, strong shaking will be felt as far north as Ogden and as far south as Provo.
- GEOLOGY -- The type of ground you are built on also has an impact. If your building is on bedrock, it will do better generally than a building in a liquefaction zone, such as much of the Salt Lake Valley. Liquefaction can do some crazy things, like causing buildings to tilt. Here is a liquefaction potential map for Salt Lake County. It was produced by our friends at Utah Geological. Read more here. Much of the Wasatch Front is built in a liquefaction zone. This is because most of our valleys in northern Utah were once part of ancient Lake Bonneville. Ancient lake bed does not always do so well under intense shaking.
- GROUND ACCELERATION -- This refers to how quickly the ground moves underneath your building. Is your building receiving the initial shock? Or is it riding some waves? A small percent of buildings out of our entire building stock will collapse. Unfortunately, a small percent is still thousands of buildings. If you are in a newer or retrofitted building, far from the epicenter, your risk is lower. The best safety action you can take during an earthquake is drop, cover and hold on until the shaking stops. People are more likely to be injured or killed by nonstructural things falling on them than by a building collapse. You can secure items such as artwork, shelves, trophies or pottery as part of your participation in this year's Great Utah Shake Out. We call it "securing your space."
There will still be many buildings that do collapse. This scientific document considers many factors in earthquake modeling and gives us an idea of what a magnitude 7.0 earthquake would do in Salt Lake. A couple of striking things from that scenario are the following:
- 2,300 fatalities
- 84,000 displaced households
- 480,000 homes without potable (drinking) water
Be Ready Utah has a version of the scenario below:
This is why we are constantly sharing preparedness ideas from our Be Ready Utah team. Preparedness = confidence. Just start by making sure you have shoes and a flashlight next to your bed.