Earthquakes are one of the most difficult natural disasters to prepare for. Despite the fact that half the world’s population lives near active faults, massive quakes are infrequent enough that many don’t realize their proximity to faults—much less what to do when an earthquake hits.
Earthquake risk zones, too, are far less discussed and publicized than flood zones, though the Federal Emergency Management Agency (FEMA) maps them. According to FEMA, there are three main factors that determine your seismic risk: the level of the seismic hazard, the number of people and amount of property exposed to said hazard, and how vulnerable these people and property are to the hazards.
Curbed spoke with experts in the field to find out what this risk formulation actually means, and how homeowners should best prepare.
Understanding seismic hazards
Some states, like California and Utah, have thousands of fault lines running underneath them that cause frequent earthquakes that are too small to even feel. “Small earthquakes are happening every day near you, and large earthquakes are happening somewhere around the globe that may not be in your mind,” says Volkan Sevilgen, the co-founder of Temblor, an app that estimates the likelihood of seismic shaking and home damage.
According to FEMA, seismic hazards are “sources of potential harm or loss during earthquakes.” These hazards can be naturally occurring phenomena, such as landslides or tsunamis, generated by the ground shaking, or they can be elements of the built environment, such as vulnerable buildings, brittle piping, or loose equipment, all of which can become hazards when exposed to shaking.
Measuring seismic hazards
Now that you know what seismic hazards are, how can you begin to measure them? First, understand how prone your area is to earthquake risk—and get as specific as possible.
“Not everyone will be affected by an earthquake on the same level,” says Sevilgen, who adds that Temblor was created in an effort to pinpoint risk based on specific locales—something FEMA’s earthquake mapping does not do.
Because seismic risk differs significantly across the United States, there are different mapping methods depending on where you live. The Central United States Earthquake Consortium, for example, tracks central states, while the Cascadia Region Earthquake Workgroup tracks those in the Pacific Northwest.
While maps can lay out fault lines and track earthquakes as they happen, they are unable to predict exactly when and where an earthquake will happen, how strong it will be, and the resulting seismic hazards.
Homeowners in earthquake-prone areas need to take the long view when assessing risk, says Sarah Sol, a spokesperson with the California Earthquake Authority, a nonprofit that provides residential earthquake insurance. “There’s a forecast of a greater than 99 percent chance of a magnitude 6.7 or greater earthquake striking California in the next 30 years,” she says. “You can tell that’s the life of a mortgage. So pretty much anywhere in the state, you’re at a pretty high risk of a significant earthquake damaging your home.”
Understanding exposure and vulnerability
The hazards of an earthquake are also highly dependent on what FEMA refers to as exposure: the number of people present in the area, plus the quantity and value of the buildings, infrastructure, and other property. The denser and more urbanized the location, the greater the risk.
During a massive quake, each element of the built environment—from buildings to highways—will weather the shaking to varying extents, depending on when it was built. Newer structures in compliance with the latest seismic building codes and standards will be more resistant to earthquake damage. Older structures built under earlier, less-effective codes, which have not been retrofitted to meet later standards, are likely to sustain more damage.
Your area risk = hazards + exposure + vulnerability
Consider these factors when trying to determine the earthquake risk of where you live: Is your home located in an area with numerous fault lines? Are you situated in a dense locale with lots of people and buildings? Is your home built to withstand a future earthquake? While some factors like city density will be out of your control, you can still protect yourself and your home.
“If you own an older house—[from] 1979 or earlier—it’s probably not built to the latest building codes,” says Sol. These are the most vulnerable types of property, and Sol recommends retrofitting them for earthquake protection, as well as purchasing earthquake insurance.
“There’s often the perception that earthquake damage is covered by traditional home insurance, and in California it isn’t,” Sol says. She also recommends a number of safety measures, like securing objects within your home that may fall during a quake, to establishing a disaster plan. “You’ll want to have some preparation in place, as an earthquake can happen without any warning at all,” she says.