Menu
Contact Us Search
Organization Title

NR 2003-08
April 17, 2003

Contact: Ed Wilson
Mark Oldfield
Don Drysdale
(916) 323-1886

EARTHQUAKES IN SACRAMENTO? IT COULD HAPPEN

SACRAMENTO – After an earthquake with an estimated magnitude of 6.6 that caused widespread damage nearby, the local newspaper’s headline read: “The Earth Dances a Lively Hornpipe.”

The paper in question wasn’t the San Francisco Chronicle, Los Angeles Times or Eureka Times-Standard, all of which have had their fair share of earthquake headlines.

It was the Sacramento Bee.

While Sacramentans undoubtedly have less to fear from earthquakes than many other Californians, the area isn’t totally immune from being shaken up at times.

The 97th anniversary of the Great San Francisco Earthquake is April 18. But there’s another anniversary of which Sacramento-area residents should be aware.

The “lively hornpipe” the Earth danced that was felt so strongly in Sacramento occurred on April 19, 1892. The epicenter was estimated to be somewhere in the heavily damaged area of Vacaville, Dixon and Winters (“Main street is a scene of desolation,” the Bee reported of Winters). There was also damage in the capital, Woodland, Chico, Davis, Napa, and Fairfield, among other places. A second destructive magnitude 6.4 quake occurred two days later, followed on April 29 by a 5.6 aftershock.

Unlike Los Angeles and San Francisco, Sacramento is not known to be underlain by active faults. However, there are many known faults all around, and perhaps some unknown ones, too.

The Foothills Fault System – which includes faults with names like Cleveland Hill, Spenceville, Deadman, Maidu, Prairie Creek and Swain Ravine – passes just east of Folsom Lake and runs through locales such as Auburn, Placerville, El Dorado Hills and Shingle Springs. The system runs from Mariposa to the Chico area. The 1975 magnitude 6.1 Oroville earthquake was caused by movement along the Cleveland Hills fault.

There is a complex zone of faults on the western side of the valley, many of which do not reach the surface. A zone of blind thrust faults is located along the western margin of the Great Valley. A segment of this fault zone may have produced the 1892 Winters-Vacaville earthquakes. Faults that are visible at the surface include the Vaca fault and the Montezuma Hills fault. Other faults have been mapped in the eastern Coast Ranges, but their earthquake potential is unknown.

To the northwest of Sacramento is the Dunnigan Hills fault, which has produced some odd-looking geography just to the west of Interstate 5. And to the south, an earthquake estimated at magnitude 6.0 hit the delta in 1889, most heavily damaging the area around Antioch, Rio Vista and Collinsville.

There are also faults closer to the Bay Area thought to be capable of generating major earthquakes: the Calaveras, Hayward, Greenville and Concord-Green Valley. All are within 60 miles of Sacramento as the crow flies; a large enough quake on any one of them would certainly be felt and could potentially cause damage in the capital.

“The 1989 Loma Prieta earthquake caused superficial damage in the Resources Building in downtown Sacramento and certainly was felt by many residents,” pointed out Michael Reichle, assistant director of the Department of Conservation’s California Geological Survey. “That was a magnitude 6.9 quake centered more than 100 miles away, near Santa Cruz. An earthquake of that size or larger on the Calaveras or Hayward fault would almost certainly cause some damage in Sacramento.”

Sacramento’s skyline was rather modest in 1989. While 14 years later no one will confuse it with Manhattan, there are several more skyscrapers. Tousson Toppozada, a senior seismologist with DOC’s California Geological Survey, said it will be interesting to see how Sacramento’s tallest buildings respond the next time there is a magnitude 7 or larger earthquake centered within 200 miles.

“Obviously, there were no 20-story buildings in town at the time of the Winters earthquake, and there were only a few when Loma Prieta struck,” Toppozada said. “There was a magnitude 7.0 earthquake 70 miles west of Cape Mendocino on September 1, 1994. That’s about 250 miles away from Sacramento, yet the seismic waves caused a great deal of motion in the top floors of our headquarters building (at 8th and K streets), and some people felt compelled to exit the building.”

Toppozada explained that tall buildings -- designed to flex in the event of earthquakes -- are more likely to be affected by the waves generated by large, distant temblors, while shorter structures are more impacted by closer quakes.

For more than a century, the foothills area was considered seismically inactive. That changed with the 1975 Oroville earthquake. The temblor didn’t cause much damage outside of the sparsely populated Oroville area, but it did have a major impact.

“The scientific community had to reassess that large area as seismically active,” Reichle said. “The foundations for the Auburn Dam were being built at the time, and for design purposes, we were asked to estimate how large an earthquake the system could generate. We estimated a magnitude 6.5, capable of displacing the dam’s foundation by about three-quarters of a foot. That sent the dam back to the drawing board. The cost multiplied over time, and the dam was never built.”

###