SACRAMENTO, CA - Rocked to the east by multiple earthquakes in the Reno area recently and always with the threat of a major shaker to the west along the Calaveras, Hayward or San Andreas faults, the Sacramento and San Joaquin valleys are not immune to a quake hazard.

Much of the interior valleys lie within the Foothills Fault system, which extends roughly from about Fresno and Mariposa in the south northwest to about Red Bluff. There are known faults but historically speaking, the region does not have the kind of fault structure that precludes significant displacement and thus ground shaking in an earthquake.

That's not to say earthquakes don't happen. In 1975 a moderate earthquake measuring magnitude 5.7 occurred near the Oroville Dam. The dam held but the event prompted further study of a dam in Auburn, about 40 miles southeast, that was in the beginning stages of construction.
In 1976, the Association of Engineering Geologists, Seismic Hazards Committee concluded that the concrete dam proposed for Auburn would fail in the event of a moderate quake like that at Oroville and construction ceased.

Geologists generally agree that even though earthquake hazard maps do not place much of the Central Valley as at great a risk as other areas of California, the impact of a major quake along the Hayward Fault which lies under the Coast Range to the west could have a definite impact in interior California.

This map from the California Geological Survey shows the probability of a major quake along faults.

There are plenty of reasons to be prepared for a big quake, which experts say is not an if, but a certainty.

Live_Online at 5 p.m. discussed our vulnerability to a significant earthquake with geophysicist Dr. Gerald Bawden of the United States Geological Survey. The interview and Q & A will be posted soon.