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Oct 21 / Dave Schumaker

Hayward – America’s Most Dangerous Fault

A few more local stories related to the Hayward fault today.

Offset Curb
An offset curb shows evidence of aseismic creep along the Hayward fault in Hayward, California. The offset is visible in the curb itself. The arrows were marked when the photo was taken to track further offset along the fault in the future. Photo by Dave Schumaker

This past week, we had a couple of notable, earthquake-related anniversaries. October 17th of course is known for the 1989 Loma Prieta earthquake, which happened right before Game 3 of the World Series and ultimately caused up to $13 billion in damages and losses.

Andrew Alden talks about another earthquake-related anniversary which happened on this day, October 21, 1868. Prior to the famous 1906 San Francisco, Earthquake, this was known as the “big one” that happened in the Bay Area.

Interestingly enough, the Hayward fault has an average recurrence interval of 140 years. Today marks 140 years exactly.

Estimated shaking intensity from the 1868 Hayward fault earthquake.
Source: USGS

The Hayward fault is the primary fault that scientists and emergency officials are worried about in the Bay Area. The BBC has an article out today titled, “America’s Most Dangerous Fault” and talks about the Hayward fault, as well as direct evidence of the fault that you can see in Hayward, California.

The first Hayward City Hall in California has long been off-limits to occupants because its foundations sit right atop an earthquake fault and it’s gradually splitting in two.

“Look up at the stairwell,” says geologist Russ Graymer, as we peer through a window.

“There are huge cracks, several centimetres broad and many metres long – basically showing the evidence that this building is being torn in half.”

The Hayward Fault is one of a network of cracks in the Earth’s surface running through the San Francisco Bay Area. The San Andreas Fault is probably the best known, but right now the Hayward is the one everyone’s talking about.

The records show that the past five large earthquakes on this fault have occurred on average about 140 years apart, and the last was – you’ve guessed it – 140 years ago. Tuesday is the anniversary.

At 0755 on the morning of 21 October, 1868, the Hayward broke with a Magnitude 6.8 quake.


“It’s the probability that the Hayward will generate a large earthquake in the next 30 years combined with the fact that it runs right through an urban area. These two facts taken together make it the most dangerous right now,” says Dr Graymer.

The comparison is often made with Kobe, Japan, which suffered a Magnitude 6.9 earthquake in 1995.

Kobe, like Hayward and Oakland, sits on the east side of a bay – Osaka Bay – and the Nojima Fault running through Kobe mirrors the Hayward in type (strike-slip) and in length.

More than 5,000 people died in the 1995 Kobe event.

Old Hayward City Hall - Fault Damage
View of damage inside the old Hayward City Hall Building, slowing being ripped apart by aseismic creep along the Hayward fault. Photo by Dave Schumaker.

See also this article from Wired today. It’s a dire situation.

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