About the Hayward Fault of California

America's Greatest Impending Earthquake Disaster

The Hayward fault is a 90 kilometer long crack in the Earth's crust that travels through the San Francisco Bay area. Its last major rupture occurred in 1868, during California's frontier days, and was the original "Great San Francisco Earthquake" until 1906.

Since then, nearly three million people have moved next to the Hayward fault with little regard for its earthquake potential. Because of the high urban density of the area it runs through and the gap in time between its most recent rupture, it is considered one of the most hazardous faults in the world. The next time it produces a large quake, the damage and destruction could be staggering - estimated economic losses from an 1868-strength earthquake (6.8 magnitude) could exceed 120 billion dollars. 

Hayward fault map
The Hayward fault (black) and its neighbors (gray). The Hayward fault (black) and its neighbors (gray). Click for full size. US Geological Survey image.

The Hayward fault is part of the wide plate boundary between the two largest lithospheric plates: the Pacific plate on the west and the North American plate on the east. The west side moves north with each major earthquake on it. Motion over millions of years has brought different sets of rocks next to each other on the fault trace.

At depth, the Hayward fault merges smoothly into the southern part of the Calaveras fault, and the two may rupture together in a larger earthquake than either could produce alone. The same may be true for the Rodgers Creek fault to the north.

The forces associated with the fault have pushed up the East Bay hills on the east and dropped down the San Francisco Bay block on the west. The California geologic map will show you more. More »

The Hayward Fault in Hayward

Hayward fault creep offset
Offset street curbs are common in downtown Hayward. Offset street curbs are common in downtown Hayward. Geology Guide photo

In 1868, the little settlement of Haywards was nearest to the epicenter of the earthquake. Today, Hayward, as it is now spelled, has a new city hall building that is built to ride on a lubricated foundation during a major quake like a kid on a skateboard. Meanwhile, much of the fault moves slowly, without earthquakes, in the form of aseismic creep. Some textbook examples of fault-related features occur in Hayward, at the center of the fault, and are easily seen within walking distance of the Bay area's light-rail line, BART.

The Hayward Fault in Oakland

creep in sidewalk
Cracked sidewalks are just one sign of fault movement in Oakland. Cracked sidewalks are just one sign of fault movement in Oakland. Geology Guide photo

North of Hayward, the city of Oakland is the largest on the Hayward fault. A major seaport and rail terminal as well as a county seat, Oakland is aware of its vulnerability and is slowly getting better prepared for the inevitable large earthquake on the Hayward fault. 

North End of the Hayward Fault, Point Pinole

Hayward fault at Pinole Point
Looking north on the fault trace at Pinole Point. Looking north on the fault trace at Pinole Point. Geology Guide photo

At its northern end, the Hayward fault runs across undeveloped land in a regional shoreline park. This is a good place to see the fault in its natural setting, where a big quake will do little more than knock you on your butt.

How Faults Are Studied

Hayward fault trench pit
A pit exposure of the Hayward fault was shown to the public. A pit exposure of the Hayward fault was shown to the public. Geology Guide photo

Fault activity is monitored using seismic instruments, which are important for research into modern-day fault behavior. But the only way to learn the history of a fault before written records is to dig tranches across it and closely study the sediments. This research, carried out in hundreds of places, has documented approximately 2000 years of large earthquakes up and down the Hayward fault. Ominously, it appears that major earthquakes have appeared with an average interval of 138 years between them over the last millennium. As of 2016, the last eruption was 148 years ago. 

The Hayward fault is a transform or strike-slip fault that moves sideways, rather than the more common faults that move up on one side and down on the other. Nearly all transform faults are in the deep sea, but the major ones on land are noteworthy and dangerous - see the Haiti Earthquake of 2010. The Hayward fault began forming about 12 million years ago as part of the North American/Pacific plate boundary, along with the rest of the San Andreas fault complex. As the complex evolved, the Hayward fault at times may have been the principal active trace, as the San Andreas fault is today—and may be again.

Transform plate boundaries are an important element of plate tectonics, the theoretical framework that explains the motions and behavior of Earth's outermost shell. More »

When a large meeting of geologists took place in the East Bay, one of the field trips organized around the occasion was a daylong tour of the Hayward fault given by geologists for geologists. I made sure to be there for this rare chance to hear, in depth and with scientific rigor, from the experts on the Hayward fault as we stood where they had worked.

Edited by Brooks Mitchell More »

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Alden, Andrew. "About the Hayward Fault of California." ThoughtCo, Jul. 1, 2017, thoughtco.com/about-the-hayward-fault-of-california-1440647. Alden, Andrew. (2017, July 1). About the Hayward Fault of California. Retrieved from https://www.thoughtco.com/about-the-hayward-fault-of-california-1440647 Alden, Andrew. "About the Hayward Fault of California." ThoughtCo. https://www.thoughtco.com/about-the-hayward-fault-of-california-1440647 (accessed November 18, 2017).