What Are the Worst U.S. Cities for Earthquakes?
June 25, 2020
So far this year, the U.S. has had four earthquakes with a magnitude greater than 5.5. They didn't happen in California, which is widely considered to be high-risk because of the San Andreas Fault. Instead, they happened in Nevada, Idaho, Utah, and Alaska.
Do you know all of the places in the country that have potential earthquake hazards?
To find out, we looked at earthquake data from the United States Geological Survey (USGS) and the long-term predictions of seismic activity via the National Seismic Hazard Maps. After considering the frequency of past earthquakes and the fault slip rates, the data reveals that a notable quake could occur in several parts of the country.
Here are the six worst places for earthquakes.
Image attribution: USGS/ Public Domain
The seismic activity in California is widely known, and high-hazard areas cover large sections of the state, including the San Francisco Bay area, Los Angeles, and San Diego.
The San Andreas Fault has caused some of the most notable earthquakes in recent memory. These quakes have been especially destructive because they occur in places where many people live. In 1994, the Northridge earthquake with a magnitude of 6.7 struck near LA, killing 57 people, injuring more than 8,700, and caused $13 to $40 billion in damages.
Significant research has been devoted to predicting the next "big one" and devising a warning system. One 2013 report estimates that every 6.7 years, somewhere in the state could have an earthquake the size of Northridge or greater.
2. Coastal Pacific Northwest
Another major fault line runs the length of the Pacific Northwest from near Vancouver to near Cape Mendicino, CA. Called the Cascadia subduction zone, a big quake along this fault could affect the cities of Seattle, Tacoma, Portland, Eugene, Salem, and Olympia.
With a full-margin rupture, the entire shelf from California to Canada could be displaced six feet down and 30 to 100 feet west, flattening the mountains and releasing the current geo-compression. FEMA predicts that a Cascadia earthquake and tsunami would injure 27,000, kill 13,000, and damage a million homes.
In the next 50 years, the odds of a big one are about 33 percent. However, even a small quake has the potential to cause property damage and disruption.
3. New Madrid, Missouri
One of the biggest earthquakes in American history occurred in the Mississippi Valley near the juncture of Missouri, Illinois, Kentucky, Tennessee, and Arkansas. The sequence of three quakes happened between 1811 and 1812, and reports say that tremors caused the Mississippi River to run backward.
The New Madrid Seismic Zone is one of the most active seismic areas east of the Rockies and has about 200 small quakes per year.
Unlike coastal fault lines, a big quake in the center of the country poses different risks. In particular, a disruption of the Mississippi River could cause severe inland flooding and levee failures. A FEMA director of the Central U.S. Earthquake Consortium told the Atlantic:
“I mean if we’re at flood stage, it’s kind of the worst-of-the-worst case scenario. So if the levees are already jeopardized either by overtopping or saturation, where the water’s been there for quite a while, and then you get a shake to it? Y’know, the river’s just gonna take the path of least resistance. And who knows whether that’s right through these communities."
He added that a massive earthquake could cause the rivers to overtake portions of southern Missouri, Arkansas, or Western Kentucky.
4. Charleston, SC
The Charleston area is at a high-risk for a damaging earthquake within the next 50 years. As a seismologist at the College of Charleston told the Post and Courier, “We are the bull’s-eye on the East Coast."
During the major Charleston earthquake of 1886, nearly every building in the city was damaged and most had to be torn down. Structural damage occurred within a several hundred-mile radius, extending throughout South Carolina and reaching as far as southern Virginia and central Ohio.
Known as the Middleton Place-Summerville Seismic Zone, the latest USGS maps have slightly increased the risk of earthquake hazards in the area. This could mean building codes will be updated and more homeowners will repair their home's foundation to protect against a seismic threat.
5. Big Island, Hawaii
Along with its active volcano, Hawaii has thousands of earthquakes every year. Most of them are small, a few can be felt, and some are large enough to cause significant damage.
An earthquake with a 5.0 to 5.9 magnitude occurs, on average, once every 1.5 years. For a 6.0 to 6.9 magnitude, the average is once every 7.7 years. A major earthquake of a 7+ magnitude happens about every 56 years.
6. Anchorage and southern Alaska shore
Alaska is one of the most seismically active places in the world. They happen frequently, with 11 percent of the world's earthquakes occurring in the state. And they are of a significant magnitude with an average of one per year at seven to eight magnitude, and a magnitude of eight or greater happening every 13 years, on average.
The active fault line, known as the Alaska-Aleutian Megathrust, makes earthquake safety a concern for everyone in the state. Support beams could crumble, unsecured homes could slide or bounce off their foundations. And the ground underneath a home could slide down an incline.
Your Home Is the Most Important Part of Earthquake Preparedness
As Oregon State University explains, "Chances are two out of three that you’ll be at home when the next big earthquake strikes, and one out of three that you’ll be in bed. So your home’s ability to withstand an earthquake affects not only your pocketbook but also your life and the lives of those who live with you."
A free inspection from the country's leading foundation repair experts can help you learn what steps you can take to secure your foundation and protect your home.