America’s Most Dangerous Fault Is Likely to Rupture in the Next 30 Years

No, it’s not the San Andreas Fault.

When people think of dangerous faults in the United States, the San Andreas fault likely comes to mind. But despite its notoriety, there is another potentially greater threat located in the East Bay region of Northern California.

It is known as the Hayward Fault, and it could produce the greatest natural disaster ever to hit the US.

Although the Hayward Fault is shorter than the San Andreas, what it lacks in potential magnitude, it makes up for with proximity to major cities, lying directly under structures where many people live and work.

The San Andreas cuts predominantly through remote areas, whereas the entire length of the Hayward Fault runs through densely populated cities such as Oakland (pop. 406,000), Fremont (pop. 224,000), and Berkeley (pop. 116,000), and is not far from San Francisco (pop. 805,000) and San Jose (pop. 945,000).

Given the Hayward’s proximity to large populations, its rupture presents a huge risk. In fact, the U.S. Geological Survey (USGS) describes the Hayward Fault as “the single most urbanized earthquake fault in the United States.”

Signs of the fault are found across the state — offset sidewalk curbs, cracking roads and homes, and even cracks in the University of California-Berkeley’s football stadium. What’s more, in 2015, the Working Group on California Earthquake Probabilities determined that there was a 72 percent chance of an earthquake occurring at the fault in the next 30 years — one that could measure a magnitude 6.7 or greater.

Creep on the Hayward Fault has broken and offset this curb in the city of Hayward. Photo credit: USGS

The last significant quake on the Hayward Fault was in October 1868, estimated at a magnitude 6.8. According to a 2012 paper published in the Bulletin of the Seismological Society of America, James Lienkaemper of USGS and colleagues determined that the fault’s recurrence interval over the last two millennia is about 161 years, plus or minus 65 years.

Since the last quake was 148 years ago, the state is currently sitting within the range.

USGS led a study back in 2008, along with URS Corporation, Lawrence Livermore National Laboratory, Stanford University, and the University of California at Berkeley, to create computer simulations of large earthquakes on the Hayward fault. The computer simulations included a total of seven earthquake scenarios: three magnitude 6.8 scenarios with different starting locations (epicenters), three magnitude 7.0 scenarios with different epicenters, and one magnitude 7.2 scenario.

One of the 7.0 magnitude scenarios, using Oakland as the starting location, can be seen here:

The Hayward Fault has the potential for immense devastation, but according to Steve Newton, geology professor at College of Marin in Kentfield, California, many people are not really aware of the danger it poses, and some do not even know where the fault is.

Although it is only a matter of time before a large earthquake on the Hayward Fault happens, how governments prepare for it is crucial and will make a big difference in the aftermath of this inevitable natural disaster.

But the science is clear: the Hayward fault is going to rupture in the future. When it will happen is unknown, but unfortunately the effects will be major shaking of infrastructure, loss of life and injuries, and economic damage.

The article appears in the June Issue of EARTH Magazine.